This is ick.info, produced by makeinfo version 4.8 from ick.txi.

INFO-DIR-SECTION INTERCAL
START-INFO-DIR-ENTRY
* C-INTERCAL: (ick).                 The C-INTERCAL language and compiler.
* ick: (ick) Invoking ick.           Invoking the C-INTERCAL compiler.
* convickt: (ick) convickt.          The command-line character set converter.
END-INFO-DIR-ENTRY

This manual is for C-INTERCAL version 0.28.  It does not replace the
old groff manual, nor is it designed to be read in conjunction with it;
instead, it serves a different purpose, of providing information useful
to users of C-INTERCAL (unlike the other manual, it is not derived from
the original INTERCAL-72 manual).

Copyright (C) 2007 Alex Smith.

     Permission is granted to copy, distribute and/or modify this
     document under the terms of the GNU Free Documentation License,
     Version 1.2 or any later version published by the Free Software
     Foundation; with no Invariant Sections, with no Front-Cover Texts,
     and with no Back-Cover Texts.  A copy of the license is included
     in the section entitled "GNU Free Documentation License."



File: ick.info,  Node: Top,  Next: About this manual,  Up: (dir)

C-INTERCAL 0.28
***************

This manual is for C-INTERCAL version 0.28.  It does not replace the
old groff manual, nor is it designed to be read in conjunction with it;
instead, it serves a different purpose, of providing information useful
to users of C-INTERCAL (unlike the other manual, it is not derived from
the original INTERCAL-72 manual).

Copyright (C) 2007 Alex Smith.

     Permission is granted to copy, distribute and/or modify this
     document under the terms of the GNU Free Documentation License,
     Version 1.2 or any later version published by the Free Software
     Foundation; with no Invariant Sections, with no Front-Cover Texts,
     and with no Back-Cover Texts.  A copy of the license is included
     in the section entitled "GNU Free Documentation License."


* Menu:

* About this manual::               What is covered in this manual

The C-INTERCAL compiler
* Installation::                    How to install C-INTERCAL
* Invoking ick::                    Options to give to the compiler ick
* Errors and Warnings::             Error messages, and what to do about them
* The yuk debugger::                How to use the runtime debugger

Basic INTERCAL features
* Syntax::                          Holding statements together
* Expressions::                     Operators, operands, and grouping
* Statements::                      What an INTERCAL statement can do
* System Library::                  Pre-existing INTERCAL routines

INTERCAL dialects and extensions
* TriINTERCAL::                     INTERCAL in non-binary bases
* Multithreading and Backtracking:: Running INTERCAL programs in parallel
* Operand Overloading::             Where one expression stands for another
* PIC-INTERCAL::                    INTERCAL on embedded systems
* CREATE::                          Creating new syntax at runtime
* External Calls::                  Linking INTERCAL with other languages
* Differences to Other Compilers::  C-INTERCAL vs. CLC-INTERCAL

Appendices and indices
* Character Sets::                  A list of character sets used by INTERCAL
* convickt::                        The command-line character set converter
* Optimizer Idiom Language::        The syntax to specify optimizer idioms
* Copying::                         License information for the code and manual
* Main Index::                      An index of all the pages in this manual


File: ick.info,  Node: About this manual,  Next: Installation,  Prev: Top,  Up: Top

About this manual
*****************

This is the Revamped Instruction Manual for C-INTERCAL (this version is
distributed with C-INTERCAL version 0.28).  It is divided into four
parts.

The first part is about the C-INTERCAL compiler `ick', and how to use
it. It covers installing the compiler, using the compiler, what error
and warning messages are produced by the compiler, and some information
on how to use the debugger.

The second part is about the core INTERCAL language, invented in 1972,
and some other commands since then which don't feel like they're
extensions.  (This is a pretty arbitrary distinction, but people who
write the documentation are entitled to arbitrary distinctions.  The
manual's licensed under a license that lets you change it (*note
Copying::), so if you disagree you can move the commands from section
to section yourself.)  Mostly only commands that are implemented in
C-INTERCAL are covered here (if you're interested in the other commands
implemented in other compilers, read CLC-INTERCAL's documentation).
However, a comprehensive guide to portability of these commands between
C-INTERCAL and other INTERCAL compilers is given.

The third part covers the INTERCAL extensions and dialects that are
implemented by C-INTERCAL, such as TriINTERCAL and Threaded INTERCAL.
Again, extensions and dialects not implemented have been mostly left
out.

The final part contains appendices (which were known as `tonsils' in
the original INTERCAL manual), such as character sets used by INTERCAL,
programs other than `ick' in the C-INTERCAL distribution, information
on how to read and update the list of optimizer idioms used by the
compiler, and the copyright.


File: ick.info,  Node: Installation,  Next: Invoking ick,  Prev: About this manual,  Up: Top

1 Installation
**************

The C-INTERCAL distribution is distributed in source code form; this
means that before using it, you first have to compile it.  Don't worry:
if you have the right software, it's not at all difficult.  Most
Linux-based and UNIX-based computers are likely to have the software
needed already; the software needed to compile source-distributed
packages is also readily available for free for other operating
systems.  The following instructions will help you install the
distribution in a method appropriate for your system.

(If you happen to be using Debian or Ubuntu, you can also obtain and
install binaries with the command `sudo apt-get install intercal',
making the rest of this chapter redundant.  If you do this, use
Debian's bug tracker to report bugs, rather than reporting them
directly to the maintainers.)

* Menu:

* Obtaining::            How to get a C-INTERCAL distribution to install
* Unpacking::            What to do with the distribution file
* Simple Installation::  Normally you can just do things the easy way
* DOS/Windows Install::  For users of DOS or of Microsoft Windows
* Not Installing::       You can use the software without installing it
* Uninstalling::         If you don't want to use the software
* Reporting Bugs::       If it doesn't work or you know how to fix it
* Distributing::         How to make your own C-INTERCAL distribution


File: ick.info,  Node: Obtaining,  Next: Unpacking,  Up: Installation

1.1 Obtaining
=============

C-INTERCAL distributions have been stored in many different places over
time; it can sometimes be hard to make sure that you are finding the
most recent version.  In order to make sure that you have the most
recent version, the easiest way is to look at the alt.lang.intercal
newsgroup; all releases of the C-INTERCAL compiler ought to be
announced there.  (If you are interested in what other INTERCAL
compilers are available, it may also be worth looking there.)  If you
don't have access to a newsreader, your newsreader doesn't cover that
newsgroup, or the distance between releases has been too large for your
news server to keep the message, it's likely that you can find the
announcement in an archive on the World Wide Web; at the time of
writing (2007), the archives of the newsgroup are stored by Google
Groups (http://groups.google.com), and a search for `alt.lang.intercal'
there should tell you where to find a copy.

If you're looking for the latest version, note that the number after the
dot represents the major version number; you want to maximise this in
favour of the number before the dot, which is the bugfix level within a
major version.  (Major versions are released as version 0.whatever; if a
new version comes out that fixes bugs but adds no new features, nowadays
its number will be of the form 1.whatever, with the same major number.
This has not always been the case, though.)


File: ick.info,  Node: Unpacking,  Next: Simple Installation,  Prev: Obtaining,  Up: Installation

1.2 Unpacking
=============

The distribution is likely to be a single file with extension `.tgz';
this refers to a gzipped tar file.  Most computer systems can extract
files in this format (nowadays even many computers running Windows have
the appropriate software).

It doesn't matter where you extract the distribution file to: it's best
if you don't put it anywhere special.  If you aren't an administrator,
you should extract the file to somewhere in your home directory (Linux
or UNIX-like systems) or to your My Documents directory (recent versions
of Windows; if you're using an older version, then you _are_ an
administrator, or at least have the same privileges, and can extract it
anywhere).  Some commands that you might use to extract it:

Generic UNIX/Linux
          gunzip ick-0-28.tgz
          tar xvf ick-0-28.tar

     On most UNIX-based and Linux-based systems, `tar' will be
     available to unpack the installation files once they've been
     uncompressed with `gunzip'.  `gunzip' is also likely to be
     available; if it isn't, you will need to download a copy from the
     Internet.

Using GNU tar
          tar xzvf ick-0-28.tgz

     If you are using the GNU version of `tar' (which is very likely on
     Linux), you can combine the two steps into one as shown here.

Using DJGPP
          djtar -x ick-0-28.tgz

     On a DOS or Windows system, you will have to install DJGPP anyway
     to be able to compile the distribution (*note DOS/Windows
     Install::), and once you've done that you will be able to use
     DJGPP's decompressing and unpacking utility to extract the files
     needed to install the distribution.  (You will need to type this
     at the command line; on Windows 95 and later, try choosing Run...
     from the start menu then typing `cmd' (or `command' if that fails)
     in the dialog box that opens to get a command prompt, which you
     can exit by typing `exit'.  After typing any command at a command
     line, press <RET> to tell the shell to execute that command.)

On Windows
     If you're running a Windows system, you could always try
     double-clicking on the ick-0-28.tgz file.  It's quite possible that
     you'll have a program installed that's capable of decompressing and
     unpacking it.  Unfortunately, I can't guess what program that
     might be, so I can't give you any instructions for using it.


Whatever method you use, you should end up with a directory created
called `ick-0.28'; this is your main installation directory where all
the processing done by the installation will be carried out.  You will
need to have that directory as the current directory during install (at
the command prompt in all the operating systems I know, you can set the
current directory by typing `cd ick-0.28').


File: ick.info,  Node: Simple Installation,  Next: DOS/Windows Install,  Prev: Unpacking,  Up: Installation

1.3 Simple Installation
=======================

There are scripts included in the distribution to automate the process
of installing, in various ways.  The simplest method of installing is to
use the following routine:

  1. Configure C-INTERCAL, by typing `sh config.sh' (or `sh
     configdj.sh' if you're using DJGPP)

  2. Compile the source code, with the command `make'

  3. Install the executables, help files, include files, and libraries,
     using `make install'.  (This is the only step that needs
     root/administrator permissions; so on a system that uses sudo to
     elevate permissions, for instance, write it as `sudo make
     install'.)


On all systems, it's worth just trying this to see if it works.  This
requires a lot of software on your computer to work, but all of it is
standard on Linux and UNIX systems.  The first command is a
shell-script which will analyse your system and set settings
accordingly; it will explain what it's doing and what settings it
detected, and create several files in the installation directory to
record its results.  (This is a configure script produced by the GNU
autoconf (config.sh is produced by the Linux version, configdj.sh by
the DJGPP version); its autoconf source code is available in the file
`config.in'.)  The second command actually compiles the source code to
produce binaries; this takes the longest of any of the steps.  You will
see all the commands that it's running as it runs them.  The third
command will copy the files it's compiled to appropriate shared
locations on your system so that anyone on the system can just use
`ick'.

There may be various factors that prevent this simple installation
method working.  On a system not based on UNIX or Linux, you may find
that you don't have some of the software required to run this (for
instance, you may be missing the shell `sh', and don't have the shell
`bash' which can emulate it, and so can't run `sh config.sh' that
depends on one of those shells being available) and so this method
won't work for you.  In such cases, one solution may be to install all
the software required; the GNU project has a version of all the
commands required, for instance, and there may be ports available for
your operating system.  However, the only software absolutely required
is a C compiler (C-INTERCAL was designed to work with `gcc' and has
only been tested in combination with that compiler, but in theory it
should be possible to adapt it to work with other compilers) and the
associated software needed to compile C files to object files and
executables, combine object files into libraries, etc.

Another possibility that might stop this process working is if your
version of the relevant software is incompatible with the GNU versions
that were used for testing.  For instance, I have come across
proprietary versions of `lex' that need directives in the source file
to say in advance how much memory the lexer-generator needs to
allocate.  In such cases, pay attention to the error messages you're
getting; normally they will suggest trivial modifications to the source
files that will cause the compilation to work again.

Some Linux and UNIX systems (notably Debian and Ubuntu) don't have the
required files for compilation installed by default.  To install them,
just download and install the required packages: for Ubuntu at the time
of writing, they are `binutils', `bison', `cpp', `flex', `gcc',
`libc6-dev', `make' to compile C-INTERCAL, and if you want to modify
it, you may also need `autoconf'.  For debugging help, you may also
want `gdb', and to recompile the documentation, you may need `groff',
`tetex-bin', `texinfo', and `tidy'.  Of course, if INTERCAL ever (the
author of this sentence was going to write something like "becomes
popular, someone will probably package up a compiler for Debian or
Ubuntu anyway", but at that point on a whim did an Ubunutu package
search for 'intercal' and actually came up with two results, which look
suspiciously like C-INTERCAL and CLC-INTERCAL, later confirming this.
The author was vaguely aware that there was a CLC-INTERCAL package
floating around, but was unaware of the C-INTERCAL package, and as a
result was too surprised to finish the sentence.)

If you're trying to do something unusual, you probably want to set some
of the settings yourself rather than letting the compilation process
guess everything.  In this case, use `sh config.sh --help' to view the
options that you can set on `config.sh'; there's a wide range of
settings that you can set available there, and one of them may be what
you want.  For the special case of a non-administrator user who wants
to test the C-INTERCAL compiler without having admin rights, or
equivalently any user who wants to test the compiler without installing
it, see *Note Not Installing::.


File: ick.info,  Node: DOS/Windows Install,  Next: Not Installing,  Prev: Simple Installation,  Up: Installation

1.4 DOS/Windows Install
=======================

On DOS and Windows, it's possible to install C-INTERCAL by using the C
compiler and utilities provided by DJGPP.  (Possibly other environments
also work, but DJGPP is the only C compilation system on which recent
versions of C-INTERCAL have been tested.)  If you don't have a copy of
DJGPP, or you're not sure whether you have the most recent version,
visit `http://www.delorie.com/djgpp'.  I think it's possible to compile
C-INTERCAL to binaries from only the files in the distribution and the C
compilation parts of DJGPP, but this relies on some prebuilt files
enclosed in the distribution, and I haven't actually tested this, so I
might be wrong.  At the other extreme, if you download and install not
only the DJGPP C compiler but also all the DJGPP ports of the GNU
utilities required to run `config.sh' and `make', you can use the
simple installation method; see *Note Simple Installation::.  (This is
actually somewhat recommended; doing this will not only allow you to
change source code, recompile, and be guaranteed to have your changes
to the source code affect the executables, and allow you to install
C-INTERCAL without having to fiddle around with the `PATH' environment
variable, but also you may then be able to install other programs
distributed in source form without further hassle.)

Assuming that you decide not to download all the utilites required to
carry out a simple install, follow the following instructions to compile
and install the C-INTERCAL compiler:

  1. If you haven't already installed DJGPP, do that now, following the
     instructions given there.

  2. Open a command prompt if you aren't at one already, unpack the
     distribution if you haven't already, and change directory to the
     main installation directory (*note Unpacking::).

  3. Run one of two commands included in the distribution especially for
     installing C-INTERCAL under DJGPP.  Which one you run depends on
     the shell you're using: if you're running under one of the
     DOS/Windows shells (`cmd.exe' or `command.com'), type
     `makeick.bat', and if you're running under a port of a UNIX or
     Linux shell (such as `bash'), type `makeick.sh'.

  4. The distribution should now have been compiled, but it still needs
     to be installed.  To do this, you will need to edit your `PATH'
     environment variable.  Under DOS and earlier versions of Windows,
     you can do this by editing `C:\autoexec.bat'; look for the last
     command that sets the `PATH' environment variable (i.e. that starts
     with `set PATH='), and add another semicolon and the `bin'
     subdirectory of your main installation directory to it (for
     instance, if your installation directory is
     `C:\stuff\intercal\ick-0.28', you want to add
     `;C:\stuff\intercal\ick-0.28\bin' to the end of that line).  Under
     later versions of Windows, this won't work (I'm not sure exactly
     where the cutoff is, but I know the other method doesn't work on
     Windows XP); instead, go via the Start menu to Settings, Control
     Panel, System, Advanced, Environment Variables, and edit either
     your own or the system-wide PATH setting (depending on whether you
     want to install for yourself or for everyone) to end with the
     `bin' subdirectory of the main installation directory, the same
     way as for older versions of Windows.


To test that the `PATH' setting is set correctly, try changing to an
unrelated directory (for instance, by typing `cd \' at a command
prompt), and typing `ick -@'; if you get a usage message for `ick',
then you've set the `PATH' setting correctly.  Note that if things go
wrong during compilation, other than errors about inability to find
`flex' or `bison' (the compilation process can succeed despite either
of these errors), it's likely that you've messed up your DJGPP
installation (maybe by setting the `PATH' or `DJDIR' environment
variables incorrectly for it).


File: ick.info,  Node: Not Installing,  Next: Uninstalling,  Prev: DOS/Windows Install,  Up: Installation

1.5 Not Installing
==================

You don't have to install C-INTERCAL to be able to use it; you can
instead stop any of the other install techniques just after compiling
the source code, before the installation step.  (This may be useful if
you just want to try out C-INTERCAL, or if you aren't a root/admin user
and therefore don't have the permissions to install things.)  When
C-INTERCAL hasn't been installed, `ick' won't be able to find the files
it looks for in the places that they ought to have been installed, so
it will look in a variety of places they might be instead (the
installation directory, if it can figure out where it is; the same
directory as the binary; the current directory).  In order for this to
work, just don't move any of the files that were compiled anywhere else.

Of course, if you haven't installed the compiler, just typing `ick' is
unlikely to work, because your computer won't know what you mean.
Instead, you should give a pathname (absolute or relative) to where
`ick' is, so that your computer can find it.  With any luck, your
computer will communicate the pathname you used to `ick' itself, and if
that happens `ick' will use it to figure out where the main
installation directory is, and find the files it needs that way.  If
you suspect that errors you are getting are due to inability to find
files (such as E127 (*note E127::) or E999 (*note E999::)), try giving
the `-u' (*note -u::) option to `ick' to see where it's looking.

You can make a `live' CD or USB-stick version of C-INTERCAL using
similar methods; configure (if possible) and compile it, but instead of
installing it, copy the entire `ick-0.28' directory to the CD or USB
stick.  INTERCAL can then be run from there by explicitly giving a
pathname to `bin/ick' or `bin/ick.exe'.


File: ick.info,  Node: Uninstalling,  Next: Reporting Bugs,  Prev: Not Installing,  Up: Installation

1.6 Uninstalling
================

It may happen that you decide to uninstall C-INTERCAL after installing
it; this may be useful if you want to test the installation system, or
change the location you install programs, or for some reason you don't
want it on your computer.  It's worth uninstalling just before you
install a new version of C-INTERCAL because this will save some disk
space; you cannot install two versions of C-INTERCAL at once (but see
*Note Not Installing:: for information on how you can use C-INTERCAL
without installing it).

If you installed C-INTERCAL using `make install', you can uninstall it
by using `make uninstall' from the installation directory, assuming
that it still exists.  If you can't use that method for some reason,
you can uninstall it by deleting the files `ick.exe' where your
computer installs binaries, `libick.a', `libickmt.a', `libickec.a', and
`libyuk.a' where your computer installs libraries, and the
subdirectories `ick-0.28' in the places where your computer installs
data files and include files, and their contents.

If you installed C-INTERCAL by changing your `PATH' environment
variable, you can uninstall by changing it back.

You can go further than uninstalling.  Running `make distr',
`districk.sh', or `districk.bat' will delete any files created by
compilation; `make distclean' will delete those files, and also any
files created by configuring.  The distribution contains prebuilt
versions of the parser, lexical analyser and OIL compiler; doing `make
clean' (or `cleanick.sh' or `cleanick.bat') will do the same thing as
`make distr' and also delete those prebuilt versions.


File: ick.info,  Node: Reporting Bugs,  Next: Distributing,  Prev: Uninstalling,  Up: Installation

1.7 Reporting Bugs
==================

If you can't get C-INTERCAL to install at all, or something goes wrong
when you're using it, reporting a bug is probably a good idea.  (This is
still important even if you figure out how to fix it, and the
information isn't in the manual, because the fix can be added to the
source code if possible, or at least to the manual, to benefit future
users.)  For general help, you may want to post to the
alt.lang.intercal news group; to report a bug or submit a patch, email
the person who released the most recent C-INTERCAL version (which you
can determine by looking at that newsgroup).

If you do find a bug (either the compiler not behaving in the way you'd
expect, or if you find a way to cause E778 (*note E778::) without
modifying the source code), it helps a lot if you can submit a bug
report explaining what causes it.  If you're not sure, say that; it
helps if you give examples of input, command line options, etc. that
cause the bug.  There are several debug options (*note Debug Options::)
that you can use to help pin down a bug if you're interested in trying
to solve the problem yourself; looking at the output C code can also
help pin down a bug if the compiler gets that far.

Information that should be given in a bug report is what you expect to
happen, what actually happens, what input and command line options you
gave to the compiler, what operating system you're using, any ideas you
might have as to what the problem is, and any appropriate debug traces
(for instance, `-H' (*note -H: -H+.) output if you think the bug is in
the optimizer).  Core dumps aren't portable between systems, so don't
send those; however, if you're getting an internal error and can dump
core with `-U' (*note -U: -U+.), it helps if you can load a debugger
(such as `gdb') on the core dump, use the debugger to produce a
backtrace, and send that backtrace.

If you figure out how to solve the bug yourself, and want to submit the
patches to help other users (this also carries the advantage that your
patches will then be maintained along with the rest of the distribution,
and that you won't have to reapply them every time you upgrade to a
newer version of C-INTERCAL), you must first agree to license your code
under the same license as the code that surrounds it (normally, that's
the GNU General Public License, but if you submit a patch to a file with
a different license, like this manual (yes, documentation patches are
useful too), you must agree to that license).  You will be credited for
the patch in the source code unless you specifically ask not to be or
you don't give your name (in both these cases, you must license the code
to the public domain so that it can be incorporated without the
attribution requirement).  Preferably, patches should be submitted in
the format created by the command `diff -u'; this command is likely to
be available on UNIX and Linux systems and versions are also available
for DOS and Windows (including a DJGPP port of the GNU version).  If
you can't manage that, just submit your new code with enough lines of
old code around it to show where it's meant to go, and a description of
approximately where in the file it was.  Patches should be submitted by
email to the person who most recently released a version of C-INTERCAL.

If you have a suggestion for a new feature, it makes sense to first
discuss it on the alt.lang.intercal news group; other INTERCAL compiler
maintainers may also want to implement that feature.  If you have
developed code to implement that feature in C-INTERCAL, you can submit
it the same way that you would submit a patch for a bug.


File: ick.info,  Node: Distributing,  Prev: Reporting Bugs,  Up: Installation

1.8 Distributing
================

Due to the licensing conditions of C-INTERCAL, you are allowed to
release your own version or distribution if you want to.  In such
cases, it's recommended that you follow the following guidelines:

  1. Make sure the new version is based on the most recent existing
     version.  Looking at the alt.lang.intercal newsgroup will normally
     let you know what version is most recent.

  2. Increment the version number; if you add any new features,
     increment the major version number (after the decimal point) and
     drop the minor version number (before the decimal point) to 0, and
     otherwise increment the minor version number.  You have to update
     the version number in the following files: `config.in',
     `config.sh', `configdj.sh', and `doc/ick.txi'.  You also have to
     rename the installation directory to reflect the new version
     number.

  3. Add an entry to the `NEWS.txt' file explaining what's new in the
     version that you're releasing, following the same format as the
     other entries.

  4. Update the `README.txt' with a description of any new files you may
     have added.

  5. Remove any autosave or backup files that may be littering the
     installation directory or its subdirectories.

  6. Run `make distclean', or `districk.sh' or `districk.bat' if you
     didn't manage to configure; this will remove all files created by
     the compilation process that shouldn't be in the distribution.

  7. Update the `MANIFEST.txt' file that lists all files in the
     distribution; on a Linux or UNIX system, you can do this by typing
     `ls -R1 > MANIFEST.txt' in the main installation directory.

  8. If creating the distribution under DJGPP, run `etc/ctrlmfix.bat'
     or `etc/ctrlmfix.sh', even if you managed to configure; this will
     sort out portability problems with newlines.

  9. Create a gzipped tar file containing the installation directory.
     Its filename should be `ick-', followed by the version number with
     the dot replaced by a dash, followed by `.tgz'; this form of
     filename is friendly to DOS.

 10. Place the new version somewhere on the Internet, and announce the
     location and the fact that a new version has been released on
     alt.lang.intercal.



File: ick.info,  Node: Invoking ick,  Next: Errors and Warnings,  Prev: Installation,  Up: Top

2 Invoking ick
**************

All operations on INTERCAL source code available in C-INTERCAL are
currently carried out by the compiler `ick'.

The syntax is

     ick -options INPUTFILE

(Options can be given preceded by separate hyphens, or all in a row
after one hyphen, or a mixture; they're all single characters.)  By
default, this compiles one INTERCAL program given as the input file
directly to an executable without doing anything fancy; usually you will
want to give options, which are described below.

* Menu:

* Language-affecting Options::       Options that specify language dialect
* Debug Options::                    Debug your code or ick itself
* Output Options::                   Specifying output format and location
* Optimizer Options::                Yes, you can optimize INTERCAL!
* Other Options::                    Options not covered in other sections
* Options to Generated Programs::    Generated executables allow options too
* Environment Variables::            What environment variables affect ick


File: ick.info,  Node: Language-affecting Options,  Next: Debug Options,  Up: Invoking ick

2.1 Language-affecting Options
==============================

The following command-line options to `ick' affect what dialect of the
INTERCAL language is compiled by the compiler; you may need to set one
or more of these options if your input is not the default C-INTERCAL but
instead some other language like INTERCAL-72 or CLC-INTERCAL, or just
because you like certainty or like being different with respect to your
output.  Note that there is no command-line option corresponding to
TriINTERCAL (or the base 4-7 versions); instead, the numeric base to
use is determined by looking at the filename extension (`.i' for base
2, the default, or `.3i' to `.7i' for the base 3-7 versions.)

`-b'
     If this option is _not_ given, there is a small chance that a
     random bug appears in the compiler, which causes the programs it
     creates to manifest a bug that causes error E774 (*note E774::).
     Giving the option means that this bug will not happen.  (You may
     wonder why this bug was preserved; it is in fact a bug that was
     carefully preserved since the days of INTERCAL-72, in this case,
     but the option to turn it off is available as a workaround.
     (There are no plans to fix this or any of the other carefully
     preserved bugs any time soon, because that would kind of defeat
     the point of having preserved them.)  Interestingly, the
     INTERCAL-72 compiler documentation mentions a similar command-line
     option that is a workaround for the same bug.)

`-m'
     This option needs to be given to allow any multithreading or
     backtracking commands or identifiers to be used.  (Unlike with
     other language features, this is not autodetected because it's
     legal to have a program with multiple COME FROM (*note COME
     FROM::) commands aiming at the same line even when it isn't
     multithreaded, in which case the commands cause error E555 (*note
     E555::) when that line is encountered (with the usual caveats
     about both commands having to be active at the time).)  Attempts
     to use non-COME FROM multithreading or backtracking commands
     without this option produce error E405 (*note E405::).

`-e'
     This option makes it possible to link non-INTERCAL programs with
     INTERCAL programs; instead of giving INTERCAL programs only on the
     command line, give one INTERCAL program, followed by any number of
     programs in other languages that have been written to be able to
     link to INTERCAL programs.  It also allows expansion libraries to
     be specified on the command line, after the INTERCAL program
     (expansion libraries are given with no extension). For more
     information, *Note External Calls::.

`-E'
     This option causes the system library to never be linked; this
     option is only useful if your program references a line number in
     the range 1000 to 1999, contains no line numbers in that range,
     and yet still doesn't want the system library to be linked in;
     therefore, it is mostly useful with `-e' when adding in a custom
     replacement system library written in a non-INTERCAL language,
     especially the expansion library `syslibc' (a system library
     replacement written in C).

`-t'
     This option tells the compiler to treat the source code as
     INTERCAL-72; as a result, any language constructs that are used
     but weren't available in 1972 will trigger error E111 (*note
     E111::).

`-a'
     This option allows the CREATE statement (*note CREATE::) to be
     used.  Note that enabling it carries a run-time penalty, as it
     means that operand overloading code has to be generated for every
     variable in the program. (This option is not necessarily needed
     for the external call version of CREATE to work, but the external
     call version has fewer features without it.)

`-v'
     It is possible to write INTERCAL code sufficiently tortuous that
     it ends up assigning to a constant.  Generally speaking, this
     isn't what you wanted to do, so the compiler will kindly cause an
     error (E277; *note E277::) that stops the insanity at that point,
     but at the cost of a significant amount of performance you can
     give this option to tell the compiler to simply change the
     constant and keep on going anyway.  (Note that unlike
     CLC-INTERCAL, this only changes uses of the constant preceded by
     `#' in your program, not things like line numbers; you want Forte
     (http://esolangs.org/wiki/Forte) for that.)  This option also
     allows you to write arbitary expressions on the left of an
     assignment statement if you wish.

`-C'
     When this option is given, the generated programs will write the
     number 4 as `IIII' rather than `IV', in case you're writing a clock
     program.

`-P'
     This tells the compiler to treat the input as PIC-INTERCAL (*note
     PIC-INTERCAL::) rather than ordinary C-INTERCAL input, and generate
     PIC output code accordingly.  There are a lot of options that are
     incompatible with this, as well as many language features, due to
     the limited memory available on a PIC.  If you get error E256
     (*note E256::), you have this option given when it shouldn't be;
     likewise, if you get error E652 (*note E652::), you should be
     using this option but aren't.  (A few simple programs are
     C-INTERCAL/PIC-INTERCAL polyglots, but such programs are incapable
     of doing input or output, meaning that they aren't particularly
     useful.)

`-X'
     The C-INTERCAL and CLC-INTERCAL compilers use different notation
     for various things, sometimes to the extent where the same
     notation is legal in both cases but has a different meaning.  As
     this is the C-INTERCAL compiler, it rather guessably uses its own
     notation by default; however, the CLC-INTERCAL notation can be
     used as the default instead using this option.  (In most
     situations where there isn't an ambiguity about what something
     means, you can use the `wrong' syntax freely.) The option causes
     ambiguous characters like `?' to be interpreted with Princeton
     rather than Atari meanings.

`-x'
     This option causes some constructs with different meanings in
     C-INTERCAL and CLC-INTERCAL to use the CLC-INTERCAL meaning rather
     than the C-INTERCAL meaning. At present, it affects the abstention
     of a GIVE UP (*note GIVE UP::) command by line number, which is
     possible as long as this switch isn't given; reading through the
     INTERCAL-72 manual, there are a lot of things that imply that this
     probably wasn't intended to be possible, but as far as I can tell
     that manual doesn't actually _say_ anywhere that this particular
     case is disallowed, even though it rules out all other similar
     cases.  It also causes I/O on array variables to be done in
     CLC-INTERCAL's extended Baudot syntax, rather than using the
     Turing Tape method.



File: ick.info,  Node: Debug Options,  Next: Output Options,  Prev: Language-affecting Options,  Up: Invoking ick

2.2 Debug Options
=================

Sometimes things will go wrong with your program, or with the way `ick'
was installed.  There may even be unknown bugs in `ick' itself (if you
find one of these, please report it).  The following options are used
to debug the whole system on various levels.

`-d'
     If you think that something has gone wrong with the parser, or you
     want to see how your program is being parsed, you can give this
     option on the command line.  All the debug output produced by the
     parser and lexical analyser will be output.

`-g'
     This option allows debugging of the final executable at the C code
     level.  Any C code generated will be left in place, and the `-g'
     option will be given to the C compiler that's used to compile the
     code, so all the information needed for a C debugger to be used on
     the executable will be present there.

`-h'
`-H'
`-hH'
     These options allow debugging of the optimiser, or produce output
     helpful for understanding how your program has been summarised.
     `-h' produces a summary of what optimiser rules were used, the
     initial expression and what it was optimised to; `-H' produces a
     more expanded view that shows each intermediate step of
     optimisation, and `-hH' shows the same output as `-H', but written
     completely using C syntax (the other options output in a strange
     mix of INTERCAL and C).

`-l'
     This option turns on generation of warnings (*note Warnings::).
     To make sure that they aren't actually useful, or are only
     marginally useful, the warning generator is far too sensitive, and
     there is no way to decide which warnings are given and which ones
     aren't; you either get all of them or none.

`-p'
     This option causes the program to run immediately after being
     compiled, and profiles the resulting program to identify
     performance bottlenecks, etc.  The usefulness of this depends on
     the resolution of the timers on the computer and operating system;
     DOS, in particular, is really bad with timer resolution.  The
     output will be saved in a file called `yuk.out' when the program
     finishes running.  It's legal to turn on both the profiler and the
     interactive debugger at the same time, but if you do this the
     profiler will also identify bottlenecks in the person typing in
     commands to step through the program! The profiler will, in fact,
     identify all the timings that particular commands in the program
     take; so `WRITE IN' instructions will often show up as taking a
     long time due to their need to wait for input.

`-w'
     This option causes the produced program to support the `printflow'
     option fully; when this option is not given, `printflow' will in
     most cases have partial or no support (except in multithreaded
     programs, where this option is redundant), because not all the
     code needed for it will be included in the program to save space.

`-u'
     When you are getting problems with finding files - for instance,
     the compiler can't find the skeleton file (*note E999::) or the
     system library (*note E127::) - this option will let you know, on
     standard error, where the compiler is looking for files.  This may
     hopefully help you pin down where the file-finding problems are
     coming from, and also offers the option of simply placing copies
     of the files where the compiler is looking as a last resort.

`-y'
     This is the main debugging option: it loads yuk, an interactive
     INTERCAL debugger with ability to step through the program, set
     breakpoints, view and modify variables, etc.  *Note yuk::.

`-U'
     The internal error E778 (*note E778::) should never happen.
     However, there are all sorts of potential problems that may come
     up, and if part of the code detects something impossible, or more
     usually when the operating system detects things have got too
     insane and segfaults, normally this error will just be generated
     and that's that.  (I most often get this when I've been writing a
     new section of code and have made a mistake; hopefully, all or at
     least most of these errors are fixed before release, though.)  If
     you want more information as to what's going on, you can give the
     `-U' option, which will cause the compiler to raise an abort
     signal when an internal error happens.  This can generally be
     caught by a debugger that's being run on `ick' itself at the time;
     on many systems, it will also cause a core dump.



File: ick.info,  Node: Output Options,  Next: Optimizer Options,  Prev: Debug Options,  Up: Invoking ick

2.3 Output Options
==================

These options allow you to control how far to compile (all the way to an
executable, or only to C, etc.), and where the output will be created.
Note that the output options may change depending on the other options
selected; for instance, many of the debug options will prevent the code
being compiled all the way to an executable.

`-c'
     By default, the original INTERCAL code will be compiled all the
     way to an executable, and the intermediate C and object files
     produced will be deleted.  Giving this option causes the compiler
     to stop when it has finished producing the C file, leaving the C
     file there as the final output of the compiler.  (Its filename is
     the same as the source file, but with `.c' as its extension/suffix
     rather than the source file's extension.)  Without this option, an
     executable will be produced with the extension changed to
     whatever's appropriate for the system you are on (or omitted
     entirely if that's appropriate for the system).

     This option also places verbose comments in the output C file.

`-o'
     This option causes the compiler to progress no further than
     producing the C output file, but instead of writing it to a file
     writes it directly to standard output.  This might occasionally be
     useful when using `ick' as part of a pipe; it can also be useful
     to see how far the compiler gets with compiling code before an
     error happens, when you're trying to track down an error.



File: ick.info,  Node: Optimizer Options,  Next: Other Options,  Prev: Output Options,  Up: Invoking ick

2.4 Optimizer Options
=====================

There are various command line options that can be used to tell `ick'
whether and in what ways to optimize code.

`-f'
     This option requests the compiler to attempt to analyse the flow
     of the program and optimize accordingly; for instance, it will
     detect which commands can't possibly be `ABSTAINED' from and
     refrain from generating code to check the abstention status of
     those commands.

`-F'
     This option tells the compiler to optimize the output for speed.
     This is done to crazy extremes; the compiler may take several
     hours/days analysing the program in some cases and still not come
     up with an improvement.  It turns on all the other optimizer
     options.  Note that not all systems accept this option, because it
     sometimes outputs a shell script disguised as an executable rather
     than an actual executable.

`-O'
     This option tells the compiler to apply optimizer idioms to the
     expressions in the code given, when appropriate.  The list of
     idioms is stored in the file `src/idiotism.oil'; note that it is
     compiled into the compiler, though, so you will have to rebuild
     and reinstall the compiler if you change it.  For more information
     about changing the list of idioms, see *Note Optimizer Idiom
     Language::.



File: ick.info,  Node: Other Options,  Next: Options to Generated Programs,  Prev: Optimizer Options,  Up: Invoking ick

2.5 Other Options
=================

Some options just can't be classified.

`-@'
     If this option is given, the compiler doesn't run at all, but
     instead prints a set of instructions for using it, explaining
     which options are available on the system you're on and which
     options conflict with which other options.



File: ick.info,  Node: Options to Generated Programs,  Next: Environment Variables,  Prev: Other Options,  Up: Invoking ick

2.6 Options to Generated Programs
=================================

Once the compiler runs and produces an output executable, that
executable itself will accept a range of options that control the way it
runs.  None of these options have to be used; a default value will be
assumed if they aren't.

`+help'
`-help'
     Whether `+' or `-' is given at the start of this option, it will
     cause the program to print out what options are available and what
     state they are in.  It will then cause the program to exit via an
     internal error.

`+wimpmode'
`-wimpmode'
     If the `+' version of this is given (rather than the default `-'),
     then the program will print a message explaining that you are a
     wimp (the mode itself is known as wimpmode), and for the rest of
     execution will input in Arabic numerals (`123' rather than `ONE
     TWO THREE') and likewise will output in Arabic numerals rather
     than Roman numerals (such as `CXXIII').  True INTERCAL programmers
     should rarely have to use this mode.

`+traditional'
`-traditional'
     This option does not actually appear to do anything.

`+instapipe'
`-instapipe'
     This option causes standard output to be flushed whenever any
     characters are output when the `+' version is used, rather than on
     each newline (the default `-' version).  It is most useful for
     more responsive pipes when outputting binary data, and also useful
     for debugging very slow programs.

`+printflow'
`-printflow'
     The usual debugging methods don't work with multithreaded or
     backtracking programs.  This option exists to give at least a slim
     chance of working out what is going on with them.  It causes the
     program to print the line number of the command it thinks it may be
     executing next (i.e. the line number that would be printed if that
     line had an error) immediately after executing each command, and
     also an internal identifier for the thread that that command was
     in.  It also prints a trace of what parts of the multithreader are
     being activated; so for instance, it will tell you when a thread
     is being forked into multiple threads or when a choicepoint has
     been deleted.  Note that the `-w' option (*note -w::) must be
     given to gain full support for flow printing in non-multithreaded
     non-backtracking programs, because otherwise the required code to
     print this information will not be generated.

`+mystery'
`-mystery'
     This option is occasionally capable of doing something, but is
     deliberately undocumented.  Normally changing it will have no
     effect, but changing it is not recommended.



File: ick.info,  Node: Environment Variables,  Prev: Options to Generated Programs,  Up: Invoking ick

2.7 Environment Variables
=========================

Various environment variables can be set to affect the operation of
`ick'.

Variable               Meaning
-------------------------------------------------------------------------- 
ICKINCLUDEDIR          These three environment variables suggest
ICKLIBDIR              locations in which `ick' should look to find
ICKDATADIR             various files that it needs: the skeleton file,
                       system library, C header files and libraries that
                       it needs, constant-output optimiser, and the GNU
                       General Public License (which the debugger needs
                       to be able to display on demand for legal
                       reasons).
CC                     The name of a C compiler to use (defaults to gcc,
                       which is the only compiler with which C-INTERCAL
                       has been tested recently).  This option has no
                       effect on DJGPP, where gcc is always used.
ICKTEMP                On DJGPP, `ick' creates temporary files to pass
TMPDIR                 options to gcc as a method of getting around the
TEMP                   limit on the length of a command line that can
TMP                    sometimes affect DOS programs.  These four
                       environment variables are tried (in this order)
                       to determine a location for the temporary file;
                       if none of them are set, the current directory is
                       used.


File: ick.info,  Node: Errors and Warnings,  Next: The yuk debugger,  Prev: Invoking ick,  Up: Top

3 Errors and Warnings
*********************

Things may go wrong, either during the compilation or the execution of
your program.  Note that some things that would be compile-time errors
in many other languages - such as syntax errors - are in fact run-time
errors in INTERCAL.

Errors and warnings appear as an error code starting with `ICL',
followed by a three digit number, followed by `I' for an error or `W'
for a warning.  However, they will be notated here as `E000', etc., to
save space and because consistency was never a strong point of
INTERCAL.  This is followed by a text description of the error, and a
hint as to the location of the error.  This is not the line on which
the error occurred, but rather the line on which the next command to be
executed is.  To add to the fun, the calculation of the next command to
be executed is done at compile-time rather than runtime, so it may be
completely wrong due to things like abstention on `COME FROM's or
computed `COME FROM's.  The moral of this story is that, if you really
want to know where the error is, use a debugger.  Note also that if the
error happens at compile-time, there is no guarantee that the line
number given makes any sense at all.  Some errors don't give next line
numbers, mostly those for which it doesn't make logical sense, such as
E633 (*note E633::).  After this is a suggestion to correct (or
reconsider) the source code and to resubnit it.  (This typo has been
carefully preserved for over a decade.)

* Menu:

* Errors::                     Error messages that might be produced
* Warnings::                   Warnings produced by the `-l' option


File: ick.info,  Node: Errors,  Next: Warnings,  Up: Errors and Warnings

3.1 Errors
==========

This is a list of the error messages that might be produced during the
compilation or execution of an INTERCAL program.

E000
     This is an unusual error; it's what's printed when a syntax error
     is encounted at runtime, in a situation in which it would be
     executed.  (An `ABSTAIN'ed syntax error, for instance, would not
     be executed; this is one of the mechanisms available for writing
     comments.)  The text of the error message is simply the statement
     that couldn't be decoded.

E017
          DO YOU EXPECT ME TO FIGURE THIS OUT?

     This error occurs when there is an attempt to use a constant with a
     value outside the onespot range; it's a compile-time error.

E079
          PROGRAMMER IS INSUFFICIENTLY POLITE

     The balance between various statement identifiers is important.
     If less than approximately one fifth of the statement identifiers
     used are the polite versions containing `PLEASE', that causes this
     error at compile time.

E099
          PROGRAMMER IS OVERLY POLITE

     Of course, the same problem can happen in the other direction; this
     error is caused at compile time if over about one third of the
     statement identifiers are the polite form.

E111
          COMMUNIST PLOT DETECTED, COMPILER IS SUICIDING

     This error happens when you give the `-t' option (*note -t::) but
     you use a language construct that wasn't available in INTERCAL-72.
     If this happens, then either there's a mistake in the program
     that prevents it being INTERCAL-72 or you shouldn't be compiling
     it as INTERCAL-72 in the first place.

E123
          PROGRAM HAS DISAPPEARED INTO THE BLACK LAGOON

     There is a hard limit of 80 `NEXT's at a time; this is to
     discourage excessive use of `NEXTING' for things like recursion.
     (Recursive programs are entirely legal; you simply have to figure
     out how to do it with computed `COME FROM' instead.  (For the
     record, it is possible.  (Using lots of nested brackets when
     talking about recursion is great (yay!).)))  Another problem with
     writing the source code that can cause this error is a failure to
     properly `FORGET' the entry on the `NEXT' stack created when
     trying to simulate a goto.

E127
          SAYING 'ABRACADABRA' WITHOUT A MAGIC WAND WON'T DO YOU ANY
          GOOD
     Your program asked to include the system library (by specifying a
     line number from 1000 to 1999 inclusive without including a line
     with that number), but due to installation problems the copmiler
     couldn't find the system library to include.  You could try using
     the `-u' (*note -u::) option to see where the compiler's looking;
     that may give you an idea of where you need to copy the system
     library so that the compilation will work.  This error happens at
     compile time and doesn't give a next command line number.

E129
          PROGRAM HAS GOTTEN LOST

     This error happens at compile time when the compiler can't figure
     out where a `NEXT' command is actually aiming (normally due to a
     typo in either the line label given or the line label on the line
     aimed for).  The logic behind this error means that the next line
     to be executed is unknown (after all, that's the whole point of
     the error) and is therefore not given.  The `-e' command-line
     option (*note -e::) makes this error into a run-time error,
     because it allows `NEXT' commands to dynamically change targets at
     runtime, as well as line labaels to dynamically change values, and
     thus the error is impossible to detect at compile time.

E139
          I WASN'T PLANNING TO GO THERE ANYWAY

     This error happens at compile time when an `ABSTAIN' or
     `REINSTATE' references a non-existent target line.  This generally
     happens for much the same reasons as E129 (*note E129::).

E182
          YOU MUST LIKE THIS LABEL A LOT!

     At present, it's impossible to have more than one line with the
     same line number.  That would make `NEXT' act too much like `COME
     FROM' in reverse to be interesting.  This error happens at compile
     time.

E197
          SO!  65535 LABELS AREN'T ENOUGH FOR YOU?

     Legal values for line labels are 1 to 65535 (with values from 1000
     to 1999 reserved if you want to use the system library, and 1600
     to 1699 reserved if you're using other expansion libraries).  This
     error comes up if you use nonpositive or twospot values for a line
     label.

E200
          NOTHING VENTURED, NOTHING GAINED

     You used a variable that isn't actually in your program.  Failing
     that (which would be quite impressive and is probably impossible,
     at least in the present version of C-INTERCAL), you specified an
     illegal number for a variable (legal numbers are positive and
     onespot).  This error happens at compile time, at least for
     illegal variable numbers.

E222
          BUMMER, DUDE!

     In INTERCAL, you're allowed to `STASH' as much as you like; this
     makes the language Turing-complete and allows for unlimited
     recursion when combined with computed `COME FROM' in the right way.
     Unfortunately, real computers aren't so idealised; if you manage to
     write a program so memory-intensive that the computer runs out of
     memory to store stashes, it causes this error at runtime.  To fix
     this error, you either have to simplify the program or upgrade
     your computer's memory, and even then that will only help to some
     extent.

E240
          ERROR HANDLER PRINTED SNIDE REMARK

     Arrays have to be large enough to hold at least one element; you
     tried to dimension an array which isn't large enough to hold any
     data.  This error happens at run time.

E241
          VARIABLES MAY NOT BE STORED IN WEST HYPERSPACE

     This error happens at run time when the subscripts given to an
     array are inconsistent with the way the array was dimensioned,
     either because there were the wrong number of subscripts or
     because a subscript was too large to fit in the array.  It can
     also happen when a multidimensional array is given to a command,
     such as `WRITE IN', that expects it to be monodimensional.

E252
          I'VE FORGOTTEN WHAT I WAS ABOUT TO SAY

     This run-time error message is caused by the compiler running out
     of memory whilst trying to do I/O; at present, it can only happen
     during CLC-INTERCAL-style I/O.

E256
          THAT'S TOO HARD FOR MY TINY BRAIN

     Some commands simply aren't available in PIC-INTERCAL.  I mean,
     PICs generally have less than a kilobyte of memory; you're not
     going to be able to use some of the more confusing language
     features with that sort of resource limitation.  The solution is
     to replace the affected command, or to not give the `-P' option
     (*note -P: -P+.) if you didn't mean to compile as PIC-INTERCAL in
     the first place.

E275
          DON'T BYTE OFF MORE THAN YOU CAN CHEW

     This error happens when there is an attempt to store a twospot
     value in a onespot variable.  The actual size of the value is what
     matters when counting its spots; so you can store the output of a
     mingle in a onespot variable if it happens to be less than or
     equal to 65535, for instance.  (This is not necessarily the case
     in versions of INTERCAL other than C-INTERCAL, though, so you have
     to be careful with portability when doing this.)

E277
          YOU CAN ONLY DISTORT THE LAWS OF MATHEMATICS SO FAR

     Reverse assignments are not always mathematically possible.  Also,
     sometimes they require changing the value of a constant; this is
     only legal if you specifically specified that it was legal by
     using the `-v' option.  In the case of an impossible reverse
     assignment (including a situation in which operand overloading
     causes a reverse assignment to happen), this error happens at
     runtime.

     This error can also come up when a scalar variable is overloaded
     to an array (which doesn't make sense, but could happen if someone
     exploited bugs in the CREATE statement (*note CREATE::)), and an
     attempt is made to read or assign to that variable.  (Subscripting
     a scalar variable is a syntax error, so there is no use for doing
     such an overload anyway.)

E281
          THAT MUCH QUOTATION AMOUNTS TO PLAGIARISM

     There is a limit of 256 on the number of nested spark/ears groups
     allowed.  If you somehow manage to exceed that limit, that will
     cause this error.  Try breaking the expression up into smaller
     expressions.  (The limit is trivial to increase by changing
     `SENESTMAX' in `ick.h'; if you ever actually come across a program
     that hits the limit but wasn't designed to, just email the
     maintainer to request a higher limit.)

E333
          YOU CAN'T HAVE EVERYTHING, WHERE WOULD YOU PUT IT?

     Your program references so many variables that the compiler
     couldn't cope.  This error is unlikely to ever happen; if it does,
     try reducing the number of variables you use by combining some
     into arrays.  This is a compile-time error.

E345
          THAT'S TOO COMPLEX FOR ME TO GRASP

     This is another compile-time error that's unlikely to ever happen;
     this one signifies the compiler itself running out of memory
     trying to compile your program.  The only solutions to this are to
     simplify your program, or to make more memory available to the
     compiler.

E404
          I'M ALL OUT OF CHOICES!

     Your program asked that a choicepoint be backtracked to or
     removed, but there aren't any choicepoints at the moment.  This
     runtime error usually indicates a logic mistake in your program.
     In backtracking programs translated from other backtracking
     languages, this indicates that the program has failed.

E405
          PROGRAM REJECTED FOR MENTAL HEALTH REASONS

     Your program used a construct that only makes sense when
     multithreading or backtracking (`WHILE', `MAYBE', `GO BACK', or `GO
     AHEAD'), but you didn't specify the `-m' option (*note -m::).  If
     you meant to write a multithreaded or backtracking program, just
     give that option; if you didn't, be careful what words you use in
     comments!  This error happens at compile-time.

E436
          THROW STICK BEFORE RETRIEVING!

     In order to `RETRIEVE' a variable, it has to be `STASH'ed first;
     if it isn't, then this error happens at runtime.

E444
          IT CAME FROM BEYOND SPACE

     A `COME FROM' aiming at a line label -- as opposed to a computed
     `COME FROM', which is allowed to be pointing at a nonexistent line
     -- must point to a valid line label.  The same applies to `NEXT
     FROM'.  This error happens at compile time if a nonexistent line
     label is found in one of these contexts.

E533
          YOU WANT MAYBE WE SHOULD IMPLEMENT 64-BIT VARIABLES?

     This error is like E275 (*note E275::), but applies when an
     attempt is made at runtime to store a threespot value (or even a
     fourspot or morespot value) in a twospot variable, or a threespot
     or greater value is produced as an intermediate during a
     calculation (for instance by a mingle operation).  No values above
     twospot are allowed at any point during an INTERCAL program; if
     you want to process higher numbers, you have to figure out a
     different way of storing them.

E555
          FLOW DIAGRAM IS EXCESSIVELY CONNECTED

     Aiming two `COME FROM's at the same line only makes sense in a
     multithreaded program.  In a non-multithread program, doing that
     will cause this error at compile time (if neither `COME FROM' is
     computed) or at run time (if the command that has just finished
     running is simultaneously the target of two or more `COME FROM's).
     This either indicates an error in your program or that you've
     forgotten to use the `-m' option (*note -m::) if you are actually
     trying to split the program into two threads.

E562
          I DO NOT COMPUTE

     The program asked for input, but for some reason it wasn't
     available.  (This is a runtime error, obviously.)   The error may
     happen because the input is being piped in from a command or file
     which has reached end-of-file, or because the user typed
     `<CTRL>-<D>' (UNIX/Linux) or `<CTRL>-<Z>' (DOS/Windows) while the
     program was trying to `WRITE IN' some data.

E579
          WHAT BASE AND/OR LANGUAGE INCLUDES STRING?

     When reading spelt-out-digit input, the input didn't seem to be a
     valid digit in English, Sanskrit, Basque, Tagalog, Classical
     Nahuatl, Georgian, Kwakiutl, Volapu"k, or Latin.  This seems to
     have languages covered pretty well; what on earth were you using,
     or did you just make a spelling mistake?

E621
          ERROR TYPE 621 ENCOUNTERED

     The compiler encountered error E621 (*note E621::).  This happens
     at runtime when the program requests that no entries are removed
     from the `NEXT' stack (which is possible), but that the last entry
     removed should be jumped to (which given the circumstances isn't,
     because no entries were removed).

E632
          THE NEXT STACK RUPTURES.  ALL DIE.  OH, THE EMBARRASSMENT!

     When an attempt is made to `RESUME' past the end of the `NEXT'
     stack, the program ends; however, this cause the program to end in
     a manner other than via `GIVE UP' or `DON'T TRY AGAIN', so an
     error message must be printed, and this is that error message.

E633
          PROGRAM FELL OFF THE EDGE

     You can't just let execution run off the end of the program.  At
     least, that is, if it doesn't end with `TRY AGAIN'.  An attempt to
     do that causes this error at runtime.  Note that if your program
     references the system library, then it counts as being appended to
     your program and so the program will run into the first line of
     the system library rather than cause this error.  As it happens,
     the first line of the system library is a syntax error, so doing
     this will cause E000 (*note E000::) with the error text `PLEASE
     KNOCK BEFORE ENTERING'.  There isn't a next statement to be
     executed with E633, so the next statement won't be given in the
     error message.

E652
          HOW DARE YOU INSULT ME!

     The `PIN' command doesn't make much sense for anything bigger than
     a PIC; using it in a non-PIC program causes this error at
     compile-time.  Try using the normal input and output mechanisms
     instead.  This error may also be a clue that you are trying to
     compile a PIC-INTERCAL program without giving the `-P' option
     (*note -P: -P+.).

E666
          COMPILER HAS INDIGESTION

     There isn't a limit on the length of an input program other than
     your computer's memory; if your computer does run out of memory
     during compilation, it causes this error.  This error can also be
     caused if too many input files are specified on the command line;
     if you suspect this is the problem, split the compilation into
     separate compilations if you can, or otherwise you may be able to
     concatenate together your input files into larger but fewer files.

E774
          RANDOM COMPILER BUG

     No compiler is perfect; sometimes errors just happen at random.
     In this case, the random error is E774.  If you don't like the
     idea that your program may be shot down by a random compiler bug,
     or you are doing something important, you can use the `-b' option
     (*note -b::) to prevent this bug happening.  (You may wonder why
     this bug is in there at all if it's so easily prevented.  The
     answer is that such a bug was present in the original INTERCAL-72
     compiler, which also had an option to turn the bug off.  It's also
     a reward for people who actually read the manual.)

E777
          A SOURCE IS A SOURCE, OF COURSE, OF COURSE

     You specified a file to compile on the command line, but the
     compiler couldn't find or couldn't open it.  This is almost
     certainly because you made a typo specifying the file.

E778
          UNEXPLANED COMPILER BUG

     This should never come up, either at compile time or at run time.
     It could come up at either when an internal check by the compiler
     or the runtime libraries realises that something has gone badly
     wrong; mistakes happen, and in such cases the mistake will have
     been detected.  (If this happens at compile time you can use the
     `-U' option (*note -U: -U+.) to cause the compiler to send an
     abort signal - which normally causes a core dump - when the error
     happens, to help debug what's causing it.)  More often, this error
     comes up when the operating system has noticed something
     impossible, like an attempt to free allocated memory twice or to
     write to a null pointer, and tells the compiler an error has
     occured, in which case the same response of putting up this error
     happens.  The point is that in all cases this error indicates a
     bug in the compiler (even if it happens at run time); in such
     cases, it would be very helpful if you figure out what caused it
     and send a bug report (*note Reporting Bugs::).

E810
          ARE ONE-CHARACTER COMMANDS TOO SHORT FOR YOU?

     This is a debug-time error caused when you give too much input to
     the debugger when all it wanted was to know what you wanted to do
     next.

E811
          PROGRAM IS TOO BADLY BROKEN TO RUN

     There's a limit to how many breakpoints you can have in a program;
     you've broken the limit and therefore broken the debugger.  This
     is a debug-time error.

E888
          I HAVE NO FILE AND I MUST SCREAM

     The output file couldn't be written, maybe because the disk is
     full or because there's already a read-only file with the same
     name.  This is a compile-time error.

E991
          YOU HAVE TOO MUCH ROPE TO HANG YOURSELF

     There is no limit on the number of threads or choicepoints that
     you can have in a multithreaded or backtracking program (in a
     program that isn't multithreaded or backtracking, these are
     obviously limited to 1 and 0 respectively).  However, your
     computer may not be able to cope; if it runs out of memory in the
     multithreader, it will cause this error at runtime.

E993
          I GAVE UP LONG AGO

     `TRY AGAIN' has to be the last command in a program, if it's there
     at all; you can't even follow it by comments, not even if you know
     in advance that they won't be `REINSTATE'd.  This error happens at
     compile time if a command is found after a `TRY AGAIN'.

E995
          DO YOU REALLY EXPECT ME TO HAVE IMPLEMENTED THAT?

     Some parts of the code haven't been written yet.  There ought to
     be no way to cause those to actually run; however, if you do
     somehow find a way to cause them to run, they will cause this
     error at compile time.

E997
          ILLEGAL POSSESSION OF A CONTROLLED UNARY OPERATOR

     Some operators (such as whirlpool (`@') and sharkfin (`^')) only
     make sense in TriINTERCAL programs, and some have a minimum base
     in which they make sense.  This error happens at compile-time if
     you try to use an operator that conflicts with the base you're in
     (such as using TriINTERCAL operators in an INTERCAL program in the
     default base 2).

E999
          NO SKELETON IN MY CLOSET, WOE IS ME!

     The skeleton file `ick-wrap.c' or `pickwrap.c' is needed to be
     able to compile INTERCAL to C.  If the compiler can't find it, it
     will give this error message.  This indicates a problem with the
     way the compiler has been installed; try using the `-u' option
     (*note -u::) to find out where it's looking (you may be able to
     place a copy of the skeleton file in one of those places).



File: ick.info,  Node: Warnings,  Prev: Errors,  Up: Errors and Warnings

3.2 Warnings
============

This is a list of the warnings stored in the warning database.
Warnings only come up when the `-l' option (*note -l::) is given; even
then, some of the warnings are not currently implemented and therefore
will never come up.

W016
          DON'T TYPE THAT SO HASTILY

     The positional precedence rules for unary operators are somewhat
     complicated, and it's easy to make a mistake.  This warning is
     meant to detect such mistakes, but is not currently implemented.

W018
          THAT WAS MEANT TO BE A JOKE

     If an INTERCAL expression has been translated from another
     language such as C, the optimiser is generally capable of
     translating it back into something similar to the original, at
     least in base 2.  When after optimisation there are still INTERCAL
     operators left in an expression, then this warning is produced.
     (Therefore, it's likely to come up quite a lot if optimisation
     isn't used!)  The system library produces some of these warnings
     (you can tell if a warning has come up in the system library
     because you'll get a line number after the end of your program).

W112
          THAT RELIES ON THE NEW WORLD ORDER

     This warning comes up whenever the compiler recognises that you've
     added some code that didn't exist in INTERCAL-72.  This allows you
     to check whether your code is valid INTERCAL-72 (although `-t'
     (*note -t::) is more useful for that); it also warns you that code
     might not be portable (because INTERCAL-72 is implemented by most
     INTERCAL compilers, but more recent language features may not be).

W128
          SYSLIB IS OPTIMIZED FOR OBUSCATION

     There is an idiom used in the system library that does a
     right-shift by selecting alternate bits from a twospot number and
     then mingling them the other way round.  A rightshift can much
     more easily be done with a single rightshift, so this is a silly
     way to do it, and this warning warns that this idiom was used.
     However, the present optimizer is incapable of recognising whether
     this problem exists or not, so the warning is not currently
     implemented.

W276
          YOU CAN'T EXPECT ME TO CHECK BACK THAT FAR

     It's an error to assign a twospot value (a value over 65535) to a
     onespot variable, or to use it as an argument to a mingle.  If the
     optimizer can't guarantee at compile time that there won't be an
     overflow, it issues this warning.  (Note that this doesn't
     necessarily mean there's a problem -- for instance, the system
     library generates some of these warnings -- only that the
     optimiser couldn't work out for sure that there wasn't a problem.)

W239
          WARNING HANDLER PRINTED SNIDE REMARK

     Your code looks like it's trying to assign 0 to an array, giving
     it no dimension; this is an error.  This warning is produced at
     compile time if it looks like a line in your code will cause this
     error, but it isn't necessarily an error because that line of code
     might never be executed.

W278
          FROM A CONTRADICTION, ANYTHING FOLLOWS

     It's sometimes impossible to reverse an assignment (a reverse
     assignment can happen if the `-v' option (*note -v::) is used and
     an expression is placed on the left of an assignment, or in
     operand overloading); if the compiler detects that a reversal
     failure is inevitable, it will cause this warning.  Note that this
     doesn't always cause an error, because the relevant code might
     never be executed.

W534
          KEEP LOOKING AT THE TOP BIT

     C-INTERCAL uses a slightly different typing mechanism to some
     other INTERCAL compilers; types are calculated at compile time
     rather than run time.  This only makes a difference in some cases
     involving unary operators.  It's impossible to detect at compile
     time for certain whether such a case has come up or not, but if
     the compiler or optimizer thinks that such a case might have come
     up, it will issue this warning.

W622
          WARNING TYPE 622 ENCOUNTERED

     Your code looks like it's trying to resume by 0; this is an error.
     This warning is produced at compile time if it looks like a line
     in your code will cause this error, but it isn't necessarily an
     error because that line of code might never be executed.



File: ick.info,  Node: The yuk debugger,  Next: Syntax,  Prev: Errors and Warnings,  Up: Top

4 The yuk debugger
******************

The C-INTERCAL distribution contains a runtime debugger called `yuk'.
Unlike most other debuggers, it is stored as object code rather than as
an executable, and it is compiled into the code rather than operating on
it.  To debug code, add `-y' (*note -y::) to the command line of `ick'
when invoking it; that tells it to compile the debugger into the code
and then execute the resulting combination.  (The resulting hybrid
debugger/input executable is deleted afterwards; this is to prevent it
being run by mistake, and to prevent spreading the debugger's licence
onto the code it was compiled with.)

yuk can also be used as a profiler using the `-p' option (*note -p::);
this produces a file `yuk.out' containing information on how much time
was spent running each command in your program, and does not prompt for
debugger commands.

Note that some command line arguments are incompatible with the
debugger, such as `-m' and `-f'.  In particular, this means that
multithreaded programs and programs that use backtracking cannot be
debugged using this method; the `+printflow' option (*note
+printflow::) to a compiled program may or may not be useful for
debugging multithreaded programs.

When the debugger starts, it will print a copyright message and a
message on how to access online help; then you can enter commands to
run/debug the program.  The debugger will show a command prompt,
`yuk007 ', to let you know you can input a command.

Here are the commands available.  Commands are single characters
followed by newlines, or followed by a line number (in decimal) and a
newline or a variable name (a `.', `,', `:' or `;' followed by a number
in decimal; note that some commands only allow onespot and twospot
variables as arguments).

Command     Description
-------------------------------------------------------------------------- 
aLINE       All non-abstained commands on line LINE become abstained from
            once.
bLINE       A breakpoint is set on line LINE.  The breakpoint causes
            execution with `c' to stop when it is reached.
c           The program is run until it ends (which also ends the
            debugger) or a breakpoint is reached.
dLINE       Any breakpoint that may be on line LINE is removed.
eLINE       An explanation of the main expression in each command on
            line LINE is printed to the screen.  The explanation is in
            the same format as the format produced by `-h' (*note -h::)
            and shows what the optimiser optimised the expression to (or
            the original expression if the optimiser wasn't used).
fLINE       Removes the effect of the `m' command on line LINE.
gLINE       Causes the current command to be the first command on LINE
            (if not on that line already) or the next command on LINE,
            as if that line was `NEXT'ed to and then that `NEXT' stack
            item was forgotten.
h           Lists 10 lines either side of the current line; if there
            aren't 10 lines to one or the other side of the current
            line, instead more lines will be shown on the other side to
            compensate, if available.
iVAR        Causes variable VAR to become `IGNORE'd, making it read-only.
jVAR        Causes variable VAR to become `REMEMBER'ed, making it no
            longer read-only.
k           Continues executing commands until the `NEXT' stack is the
            same size or smaller than it was before.  In other words, if
            the current command is not a `NEXT' and doesn't have a `NEXT
            FROM' aiming at it, one command is executed; but if a `NEXT'
            does happen, execution will continue until that `NEXT'
            returns or is forgotten.  A breakpoint or the end of the
            program also end this.
lLINE       Lists 10 lines of source code either side of line LINE, the
            same way as with `h', but using a line stated in the command
            rather than the current line.
mLINE       Produces a message onscreen every time a command on line
            LINE is executed, but without interrupting the program.
n           Show the `NEXT' stack on the screen.
o           Continue executing commands until the `NEXT' stack is smaller
            than it was before.  If you are using `NEXT's like
            procedures, then this effectively means that the procedure
            will run until it returns.  A breakpoint or the end of the
            program also end this.
p           Displays the value of all onespot and twospot variables.
q           Aborts the current program and exits the debugger.
rLINE       Reinstates once all abstained commands on line LINE.
s           Executes one command.
t           Continues execution until the end of the program or a
            breakpoint: each command that executes is displayed while
            this command is running.
uLINE       Continues execution of the program until just before a
            command on line LINE is run (or a breakpoint or the end of
            the program).
vVAR        Adds a `view' on variable VAR (which must be onespot or
            twospot), causing its value to be displayed on the screen
            whenever a command is printed on screen (for instance,
            because the command has just been stepped past, or due to
            the `m' or `t' commands).
w           Displays the current line and current command onscreen.
xVAR        Removes any view and any action that may be associated with
            it on variable VAR (which must be onespot or twospot).
yVAR        Adds a view on variable VAR; also causes a break, as if a
            breakpoint was reached, whenever the value of that variable
            changes.
zVAR        Adds a view on variable VAR; also causes a break, as if a
            breakpoint was reached, whenever that variable's value
            becomes 0.
VAR         A onespot or twospot variable written by itself prints out
            the value of that variable.
<VAR        `WRITEs IN' a new value for variable VAR.  Note that input
            must be in the normal `ONE TWO THREE' format; input in any
            other format will cause error E579 (*note E579::) and as
            that is a fatal error, the debugger and program it's
            debugging will end.
*           Displays the license conditions under which `ick' is
            distributed.
?           Displays a summary of what each command does.  (`@' does the
            same thing.)

While the code is executing (for instance, during a `c', `k', `o', `t'
or `u' command), it's possible to interrupt it with `<CTRL>-<C>' (on
UNIX/Linux) or `<CTRL>-<BREAK>' (on Windows/DOS); this will cause the
current command to finish running and the debugger prompt to come back
up.


File: ick.info,  Node: Syntax,  Next: Expressions,  Prev: The yuk debugger,  Up: Top

5 Syntax
********

INTERCAL programs consist of a list of statements.  Execution of a
program starts with its first statement; generally speaking each
statement runs after the previous statement, although many situations
can change this.

Whitespace is generally insignificant in INTERCAL programs; it cannot be
added in the middle of a keyword (unless the keyword contains whitespace
itself) or inside a decimal number, but it can be added more or less
anywhere else, and it can be removed from anywhere in the program as
well.

An INTERCAL statement consists of an optional line label, a statement
identifier, an optional execution chance, the statement itself (*note
Statements::), and optionally `ONCE' or `AGAIN'.

* Menu:

* Princeton and Atari Syntax:: There are two syntaxes for INTERCAL
* Line Labels::                Allowing lines to be referred to
* Statement Identifiers::      Marking the start of a statement
* Execution Chance::           Statements that might not execute
* ONCE and AGAIN::             Self-abstaining and self-reinstating statements


File: ick.info,  Node: Princeton and Atari Syntax,  Next: Line Labels,  Up: Syntax

5.1 Princeton and Atari Syntax
==============================

The history of INTERCAL is plagued with multiple syntaxes and character
sets.  The result has settled down with two versions of the syntax; the
original Princeton syntax, and the Atari syntax (which is more suited
to the operating systems of today).

Princeton syntax
----------------

INTERCAL-72       C-INTERCAL        CLC-INTERCAL      J-INTERCAL
------------------------------------------------------------------------ 
some versions     version 0.18+     all versions      no

The original INTERCAL-72 compiler was the Princeton compiler, which
introduced what has become known as the Princeton syntax for INTERCAL;
this is the syntax used in the original manual, for instance, and can
be considered to be the `original' or `official' INTERCAL syntax.  It
is notable for containing various characters not found in some
character sets; for instance, it writes the operator for mingle as a
cent sign (known as `change').  The other operator that often causes
problems is the bookworm operator `V', backspace, `-', which is used
for exclusive-or; the backspace can cause problems on some systems
(which was probably the original intention).  This syntax is also the
default syntax in the CLC-INTERCAL compiler, which is the de facto
standard for expanding the Princeton syntax to modern INTERCAL features
that are not found in INTERCAL-72; however, it does not appear to have
been used as the default syntax in any other compilers.  Nowadays,
there are other ways to write the required characters than using
backspace; for instance, the cent sign appears in Latin-1 and UTF-8,
and there are various characters that approximate bookworms (for
instance, CLC-INTERCAL uses the Latin-1 yen symbol for this, which just
to make things confusing, refers to a mingle in modern Atari syntax).

Atari syntax
------------

INTERCAL-72       C-INTERCAL        CLC-INTERCAL      J-INTERCAL
------------------------------------------------------------------------ 
some versions     yes               version 0.05+     yes

The other main syntax is the Atari syntax, so called because it was
originally used by the "Atari implementation" of INTERCAL-72.  It is not
clear why the implementation was given this name, because the authors
of the implementation are not known; it is not clear whether it has any
connection with Atari other than running on an Atari computer, for
instance.  The syntax was designed to work better on ASCII-based
systems, by avoiding the change character (although it can still be
written as `c', backspace, `/', which the Atari compiler documentation
claims that the Princeton compiler supported) in favour of a `big
money' character (`$'), and using the `what' (`?') as an alternative
character for exclusive-or.  This is the syntax that C-INTERCAL and
J-INTERCAL have always used, and is the one most commonly used for
communicating INTERCAL programs on Usenet and other similar fora (where
ASCII is one of the most reliable-to-send character sets).  It is also
the syntax used for examples in this manual, for much the same reason.
The Atari syntax for constructs more modern than INTERCAL-72 is
normally taken to be that used by the C-INTERCAL compiler, because it is
the only Atari-syntax-based compiler that contains non-INTERCAL-72
constructs that actually need their own notation.


File: ick.info,  Node: Line Labels,  Next: Statement Identifiers,  Prev: Princeton and Atari Syntax,  Up: Syntax

5.2 Line Labels
===============

INTERCAL-72       C-INTERCAL        CLC-INTERCAL      J-INTERCAL
------------------------------------------------------------------------ 
yes               all versions      all versions      all versions

The first part of an INTERCAL statement is a line label that specifies
what its line number is.  This is optional; it's allowed to have a
statement without a line number, although that prevents other commands
referring to it by number.  Line numbers must be constants, and unique
within the program.  However, they do not have to be in order; unlike
some other languages with line numbers, a line with a higher number can
come earlier in the program than a line with a lower number, and the
numbers don't affect the order in which commands are executed.

A line label is a integer expressed in decimal within a wax/wane pair
(`(' and `)').  For instance, this is a valid line label:

     (1000)

Note that line numbers from 1000 to 1999 are used by the system library,
so using them within your own programs may produce unexpected errors if
the system library is included.  Apart from this, line numbers from 1 to
65535 are allowed.

It has become reasonably customary for people writing INTERCAL libraries
to pick a range of 1000 line numbers (for instance, 3000 to 3999) and
stick to that range for all line numbers used in the program (apart from
when calling the system library), so if you want to write an INTERCAL
library, it may be a good idea to look at the existing libraries (in the
`pit/lib' directory in the C-INTERCAL distribution) and choose a range
of numbers that nobody else has used.  If you aren't writing a library,
it may be a good idea to avoid such number ranges (that is, use only
line numbers below 1000 or very high numbers that are unlikely to be
used by libraries in the future), so that you can easily add libraries
to your program without renumbering in the future.


File: ick.info,  Node: Statement Identifiers,  Next: Execution Chance,  Prev: Line Labels,  Up: Syntax

5.3 Statement Identifiers
=========================

INTERCAL-72       C-INTERCAL        CLC-INTERCAL      J-INTERCAL
------------------------------------------------------------------------ 
yes               all versions      all versions      all versions

After the line label (if a statement has one) comes the statement
identifier, which marks where the statement starts.  Either the label or
the statement identifier, whichever one comes first, marks where the
preceding statement finishes.

The main statement identifier is `DO'.  It also has two synonyms,
`PLEASE' and `PLEASE DO'; these synonyms are the 'polite' forms of
statement identifiers.  Although the three identifiers have the same
meaning, using either polite or non-polite identifiers too much can
cause an error; the correct proportion is approximately 3 non-polite
identifiers for every polite identifier used.  None of these identifiers
actually does anything else apart from marking where the statement
starts; they leave the statements in the default `reinstated' state.

Adding `NOT' or `N'T' to the end of any of these identifiers, to create
a statement identifier such as `DO NOT' or `PLEASE DON'T', also creates
a valid statement identifier.  These differ in meanings from the
previous set of identifiers, though; they cause the statement they
precede to not be executed by default; that is, the command will be
skipped during execution (this is known as the `abstained' state).
This applies even if the command in question is in fact a syntax error,
thus causing this to be a useful method of writing comments.  One
common idiom is to write code like this:

     PLEASE NOTE: This is a comment.

The statement identifier (`PLEASE NOT') is the only part of this
statement that is valid INTERCAL; however, because the statement
identifier is in the negated form that contains `NOT', the syntax error
won't be executed, and therefore this is a valid statement.  (In
INTERCAL, syntax errors happen at runtime, so a program containing a
statement like `DOUBT THIS WILL WORK' will still compile, and will not
end due to the syntax error unless that statement is actually executed.
*Note E000::.)

The `ABSTAIN' and `REINSTATE' statements can override the `NOT' or
otherwise on a statement identifier; see *Note ABSTAIN::.

In backtracking programs, `MAYBE' is also a valid statement identifier;
see *Note MAYBE::.  It comes before the other keywords in the statement
identifier, and an implicit `DO' is added if there wasn't one already
in the statement identifier (so `MAYBE', `MAYBE DO', `MAYBE DON'T',
`MAYBE PLEASE', and so on are all valid statement identifiers).


File: ick.info,  Node: Execution Chance,  Next: ONCE and AGAIN,  Prev: Statement Identifiers,  Up: Syntax

5.4 Execution Chance
====================

INTERCAL-72       C-INTERCAL        CLC-INTERCAL      J-INTERCAL
------------------------------------------------------------------------ 
yes               all versions      version 0.02+     all versions

It's possible to specify that a command should be run only a certain
proportion of the time, at random.  This is a rarely used feature of
INTERCAL, although it is the only way to introduce randomness into a
program.  (The C-INTERCAL compiler approximates this with
pseudorandomness.)  An execution chance specification comes immediately
after the statement identifier, but before the rest of the statement,
and consists of a double-oh-seven (`%') followed by an integer from 1
to 99 inclusive, written in decimal; this gives the percentage chance
of the statement running.  The execution chance only acts to prevent a
statement running when it otherwise would have run; it cannot cause a
statement that would otherwise not have run to run.  For instance, the
statement `DO %40 WRITE OUT #1' has a 40% chance of writing out `I',
but the statement `DON'T %40 WRITE OUT #1' has no chance of writing out
`I' or anything else, because the `N'T' prevents it running and the
double-oh-seven cannot override that.


File: ick.info,  Node: ONCE and AGAIN,  Prev: Execution Chance,  Up: Syntax

5.5 ONCE and AGAIN
==================

INTERCAL-72       C-INTERCAL        CLC-INTERCAL      J-INTERCAL
------------------------------------------------------------------------ 
no                version 0.25+     no                no

The last part of a statement is an optional `ONCE' or `AGAIN'.  `ONCE'
specifies that the statement is self-abstaining or self-reinstating
(this will be explained below); `AGAIN' specifies that the statement
should behave like it has already self-reinstated or self-abstained.
Whether the behaviour is self-abstention or self-reinstatement depends
on whether the statement was initially abstained or not; a `ONCE' on an
initially reinstated statement or `AGAIN' on an initially abstained
statement indicates a self-abstention, and a `ONCE' on an initially
abstained statement or `AGAIN' on an initially reinstated statement
indicates a self-reinstatement.

The first time a self-abstaining statement is encountered, it is
executed as normal, but the statement is then abstained from and
therefore will not run in future.  Likewise, the first time
self-reinstating statement is encountered, it is not executed (as is
normal for an abstained statement), but then becomes reinstated and will
run in future.  In each of these cases, the `ONCE' effectively changes
to an `AGAIN'; the `ONCE' only happens once, as might be expected.

`REINSTATING' a currently abstained self-abstaining statement or
`ABSTAINING' (that is, with the `ABSTAIN' or `REINSTATE' commands) a
currently reinstated self-reinstating statement causes the `AGAIN' on
the statement to change back into a `ONCE', so the statement will again
self-abstain or self-reinstate.  Likewise, `REINSTATING' a currently
abstained self-reinstating statement or `ABSTAINING' a currently
reinstated self-abstaining statement causes its `ONCE' to turn into an
`AGAIN'.

Historical note: `ONCE' was devised by Malcom Ryan as a method of
allowing synchronisation between threads in a multithreaded program
(`ONCE' is atomic with the statement it modifies, that is, there is no
chance that threads will change between the statement and the `ONCE').
`AGAIN' was added to Malcom Ryan's Threaded Intercal standard on the
suggestion of Kyle Dean, as a method of adding extra flexibility (and
to allow the `ONCE's to happen multiple times, which is needed to
implement some multithreaded algorithms).


File: ick.info,  Node: Expressions,  Next: Statements,  Prev: Syntax,  Up: Top

6 Expressions
*************

Many INTERCAL statements take expressions as arguments.  Expressions are
made up out of operands and operators between them.  Note that there is
no operator precedence in INTERCAL; different compilers resolve
ambiguities different ways, and some versions of some compilers
(including the original INTERCAL-72 compiler) will cause error messages
on compiling or executing an ambiguous expression, so it's safest to
fully group each expression.

* Menu:

* Constants and Variables::      The basic operands that make up expressions
* Grouping Rules::               How to specify grouping in expressions
* Operators::                    Joining operands into more complex expressions


File: ick.info,  Node: Constants and Variables,  Next: Grouping Rules,  Up: Expressions

6.1 Constants and Variables
===========================

INTERCAL-72       C-INTERCAL        CLC-INTERCAL      J-INTERCAL
------------------------------------------------------------------------ 
yes               all versions      all versions      all versions

The basic operands in INTERCAL are constants and variables.  These
together make up what in other languages are known as `lvalues', that
is, operands to which values can be assigned.  (Constants can also be
lvalues in INTERCAL, but by default C-INTERCAL turns this off because it
carries an efficiency penalty and can be confusing; this can be turned
on with the `-v' option (*note -v::).)

Constants can have any integer value from 0 to 65535 inclusive; higher
values (up to 4294967295) can be generated in programs, but cannot be
specified literally as constants.  (The usual way to work around this
limitation is to interleave two constants together; see *Note
Mingle::.) A constant is written as a mesh (`#') followed by a number in
decimal.  At the start of the program, all constants have the same value
as the number that identifies them; for instance, `#100' has 100 as its
value, and it's strongly advised not to change the value of a constant
during the execution of a program.

There are four types of variable: 16-bit and 32-bit unsigned integers,
and arrays of 16-bit and 32-bit unsigned integers.  These are
represented with a spot, twospot, tail, and hybrid (`.', `:', `,', and
`;') respectively.  For this reason, integers within the range 0 to
65535 inclusive are known as `onespot numbers', and integers within the
range 0 to 4294967295 inclusive are known as `twospot numbers';
variables with those ranges are known as onespot and twospot variables.
(Note that arrays did not work in C-INTERCAL before version 0.7.)

Variables are represented with a character representing their data type,
followed by an integer from 1 to 65535 inclusive, written in decimal.
Non-array variables don't need to be declared before they are used; they
automatically exist in any program that uses them.  For instance, `.1'
and `.001' are the same variable, onespot number 1.  Array variables
need to be dimensioned before they are used, by assigning dimensions to
them; see *Note Calculate::.


File: ick.info,  Node: Grouping Rules,  Next: Operators,  Prev: Constants and Variables,  Up: Expressions

6.2 Grouping Rules
==================

Because there are no operator precedences in INTERCAL, there are various
solutions to specifying what precedences actually are.

The portable solution
     All known versions of INTERCAL accept the INTERCAL-72 grouping
     rules.  These state that it's possible to specify that an operator
     takes precedence by grouping it inside sparks (`'') or rabbit-ears
     (`"'), the same way as wax/wane pairs (parentheses) are used in
     other programming languages.  INTERCAL-72 and earlier C-INTERCAL
     versions demanded that expressions were grouped fully like this,
     and this practice is still recommended because it leads to
     portable programs and is easier to understand.  Whether sparks or
     rabbit-ears (often called just `ears' for short) are used normally
     doesn't matter, and programmers can use one or the other for
     clarity or for aesthetic appeal.  (One common technique is to use
     just sparks at the outermost level of grouping, just ears at the
     next level, just sparks at the next level, and so on; but
     expressions like `''#1~#2'~"#3~#4"'~#5' are completely
     unambiguous, at least to the compiler.)

     There are, however, some complicated situations involving arrays
     subscripting where it is necessary to use sparks and ears at
     alternate levels, if you want to write a portable program.  This
     limitation is in C-INTERCAL to simplify the parsing process;
     INTERCAL-72 has the same limitation, probably for the same reason.
     Compare these two statements:

          DO .1 <- ,3SUB",2SUB.1".2
          DO .1 <- ,3SUB",2SUB.1".2~.3"".4

     The problem is that in the first statement, the ears close a
     group, and in the second statement, the ears open a group, and
     it's impossible to tell the difference without unlimited lookahead
     in the expression.  Therefore, in similar situations (to be
     precise, in situations where a group is opened inside an array
     subscript), it's necessary to use the other grouping character to
     the one that opened the current group if you want a portable
     program.

     One final comment about sparks and rabbit-ears; if the next
     character in the program is a spot, as often happens because
     onespot variables are common choices for operands, a spark and the
     following spot can be combined into a wow (`!').  Unfortunately,
     none of the character sets that C-INTERCAL accepts as input
     (UTF-8, Latin-1, and ASCII-7) contain the rabbit character,
     although the Hollerith input format that CLC-INTERCAL can use does.

Positional precedences: CLC-INTERCAL rules
     The precedence rules used by CLC-INTERCAL for grouping when full
     grouping isn't used are simple to explain: the largest part of the
     input that looks like an expression is taken to be that
     expression.  The main practical upshot of this is that binary
     operators right-associate; that is, `.1~.2~.3' is equivalent to
     `.1~'.2~.3''.  C-INTERCAL versions 0.26 and later also
     right-associate binary operators so as to produce the same results
     as CLC-INTERCAL rules in this situation, but as nobody has yet
     tried to work out what the other implications of CLC-INTERCAL
     rules are they are not emulated in C-INTERCAL, except possibly by
     chance.

Prefix and infix unary operators
     In INTERCAL-72 and versions of C-INTERCAL before 0.26, unary
     operators were always in the `infix' position.  (If you're
     confused about how you can have an infix unary operator: they go
     one character inside a group that they apply to, or one character
     after the start of a constant or variable representation; so for
     instance, to portably apply the unary operator `&' to the variable
     `:1', write `:&1', and to portably apply it to the expression
     `'.1~.2'', write `'&.1~.2''.)  CLC-INTERCAL, and versions of
     C-INTERCAL from 0.26 onwards, allow the `prefix' position of a
     unary operator, which is just before whatever it applies to (as in
     `&:1').  This leads to ambiguities as to whether an operator is
     prefix or infix.  The portable solution is, of course, to use only
     infix operators and fully group everything, but when writing for
     recent versions of C-INTERCAL, it's possible to rely on its
     grouping rule, which is: unary operators are interpreted as infix
     where possible, but at most one infix operator is allowed to apply
     to each variable, constant, or group, and infix operators can't
     apply to anything else.  So for instance, the C-INTERCAL
     `'&&&.1~.2'' is equivalent to the portable `'&"&.&1"~.2'' (or the
     more readable version of this, `"&'"&.&1"~.2'"', which is also
     portable).  If these rules are counter-intuitive to you, remember
     that this is INTERCAL we're talking about; note also that this
     rule is unique to C-INTERCAL, at least at the time of writing, and
     in particular CLC-INTERCAL is likely to interpret this expression
     differently.



File: ick.info,  Node: Operators,  Prev: Grouping Rules,  Up: Expressions

6.3 Operators
=============

Operators are used to operate on operands, to produce more complicated
expressions that actually calculate something rather than just fetch
information from memory.  There are two types of operators, unary and
binary operators, which operate on one and two arguments respectively.
Binary operators are always written between their two operands; to
portably write a unary operator, it should be in the `infix' position,
one character after the start of its operand; see *Note Prefix and
infix unary operators:: for the full details of how to write unary
operators portably, and how else you can use them if you aren't aiming
for portability.  This section only describes INTERCAL-72 operators;
many INTERCAL extensions add their own operators.

* Menu:

* Mingle::                   Interleaving bits in two operands
* Select::                   Selecting from one operand according to another
* Unary Binary Logic::       Binary logic on adjacent bits of an operand
* Array Subscript::          Selecting elements of arrays


File: ick.info,  Node: Mingle,  Next: Select,  Up: Operators

6.3.1 Mingle
------------

INTERCAL-72       C-INTERCAL        CLC-INTERCAL      J-INTERCAL
------------------------------------------------------------------------ 
yes               all versions      all versions      all versions

Mingle, or interleave, is one of the two binary operators in
INTERCAL-72.  However, different INTERCAL compilers represent it in
different ways, so it is impossible to write a mingle in a program
completely portably, because it differs between Princeton and Atari
syntax, and worse, the sequence of character codes needed to represent
it in each syntax has varied from compiler to compiler.

The original INTERCAL-72 compiler (the Princeton compiler) used the
'change' (cent) character for a mingle, represented as `c', backspace,
`/'.  (By the way, this is still the most portable way to write a
mingle; both C-INTERCAL and CLC-INTERCAL accept it, at least if a
lowercase `c' is used, the Atari compiler accepted it, and its
documentation claimed that the Princeton compiler also accepted it;
CLC-INTERCAL also accepts a capital `C' before the backspace and `/',
and allows `|' rather than `/'.)  The Atari compiler, another
INTERCAL-72 compiler, used a 'big money' character (`$') as the mingle
character; this character is also the only one accepted for mingle by
the J-INTERCAL compiler.  C-INTERCAL originally also used the `$'
character for mingle, and this character is the one most commonly seen
in existing C-INTERCAL programs, and most often used when giving
examples of INTERCAL on Usenet, because it exists in the ASCII-7
character set, and because it doesn't contain control characters.  From
version 0.18 of C-INTERCAL onwards, various other units of currency
(change, quid, and zlotnik if Latin-1 is used as the input, and euro if
Latin-9 is used as the input) are accepted; from version 0.20 onwards,
in addition to the Latin-1 characters, all the currency symbols in
Unicode are accepted if UTF-8 is used as the input format.
CLC-INTERCAL has always used the change character (either the Latin-1
version or the version that contains a backspace) for mingle.  In this
manual, mingle will be represented as `$', but it's important to bear
in mind that this character is not the most portable choice.

The mingle operator should be applied to two operands or expressions.
To be portable, the operands must both be onespot expressions, that is
expressions which have a 16-bit result; C-INTERCAL relaxes this rule
slightly and only requires that the result be in the onespot range.
(This is because the data type of a select operator's value is meant to
be determined at runtime; C-INTERCAL determines all data types at
compile time, so has to guess a 32-bit result for a select with a
32-bit type as its right operand even when the result might actually
turn out to be of a 16-bit type, and so this behaviour prevents an
error when a select operation returns a value with a 16-bit data type
and is used as an argument to a mingle.)  The result is a 32-bit value
(that is, it is of a 32-bit data type, even if its value fits into the
onespot range), which consists of bits alternated from the two
arguments; to be precise, its most significant bit is the most
significant bit of its first argument, its second most significant bit
is the most significant bit of its second argument, its third most
significant bit is the second most significant bit of its first
argument, and so on until its least significant bit, which is the least
significant bit of its second argument.

One of the most common uses of interleaving is to create a constant with
a value greater than 65535; for instance, 65536 is `#256$#0'.  It is
also commonly used in expressions that need to produce 32-bit results;
except in some simple cases, this is usually coded by calculating
separately the odd-numbered and even-numbered bits of the result, and
mingling them together at the end.  It is also used in expressions that
need to left-shift values or perform similar value-increasing
operations, as none of the other operators can easily do this; and
mingle results are commonly used as the argument to unary binary logic
operators, because this causes them to behave more like the binary
logic operators found in some other languages.


File: ick.info,  Node: Select,  Next: Unary Binary Logic,  Prev: Mingle,  Up: Operators

6.3.2 Select
------------

INTERCAL-72       C-INTERCAL        CLC-INTERCAL      J-INTERCAL
------------------------------------------------------------------------ 
yes               all versions      all versions      all versions

The select operator is one of the two binary operators in INTERCAL-72;
unlike mingle, every known implementation of INTERCAL ever has used the
sqiggle character (`~') as the representation of the select operator,
meaning that writing it portably is easy.

The select operator takes two arguments, which can be of either
datatype (that is, 16- or 32-bit).  It returns a value made by
selecting certain bits of its first operand indicated by the second
operand, and right-justifying them.  What it does is that it ignores
all the bits of the first operand where the second operand has a 0 as
the corresponding bit, that is, deletes them from a copy of the
operand's value; the bits that are left are squashed together towards
the least-significant end of the number, and the result is filled with
0s to make it up to 16 or 32 bits.  (In INTERCAL-72 the minimum multiple
of 16 bits possible that the result fits into is chosen, although if :1
has the value 131061 (in hex, 1FFFF) the expression `#21~:1' produces a
32-bit result because 17 bits were selected, even though many of the
leading bits were zeros; in C-INTERCAL the data type of the result is
the same as of the right operand of the select, so that it can be
determined at compile time, and so using a unary binary logic operator
on the result of select when the right operand has a 32-bit type is
nonportable and not recommended.)  As an example, `#21~:1' produces 21
as its result if :1 has the value 131061, 10 as its result if :1 has
the value 30 (1E in hex; the least significant bit of 21 is removed
because it corresponds to a 0 in :1), and 7 as its result if :1 has the
value 21 (because three bits in 21 are set, and those three bits from
21 are therefore selected by 21).

Select is used for right-shifts, to select every second bit from a
number (either to produce what will eventually become an argument to
mingle, or to interpret the result of a unary binary logic operator, or
occasionally both), to test if a number is zero or not (by selecting it
from itself and selecting 1 from the result), in some cases as a limited
version of bitwise-and (that only works if the right operand is 1 less
than a power of 2), and for many other purposes.


File: ick.info,  Node: Unary Binary Logic,  Next: Array Subscript,  Prev: Select,  Up: Operators

6.3.3 Unary Binary Logic
------------------------

INTERCAL-72       C-INTERCAL        CLC-INTERCAL      J-INTERCAL
------------------------------------------------------------------------ 
yes               all versions      all versions      all versions

There are three unary operators in INTERCAL-72, each of which carries
out a binary logic operation on adjacent bits of the number. The
operators are and, or, and exclusive or; and and or are represented by
an ampersand (`&') and book (`V') respectively, and exclusive or has
the same notational problems as mingle, as it differs between Princeton
and Atari syntax.  It was represented by a bookworm, written `V',
backspace, `-', in the Princeton INTERCAL-72 implementation, and this
is still the most portable way to write it (C-INTERCAL and CLC-INTERCAL
accept it).  The Atari implementation of INTERCAL-72 wrote it with a
what (`?'), and this is the representation originally used by
C-INTERCAL (and still accepted), the only representation accepted by
J-INTERCAL, the one most commonly used on Usenet, and the one used in
this manual (although again, it's worth pointing out that this isn't
portable).  CLC-INTERCAL approximates a bookworm with the yen
character, which being a currency character is one of the possible
representations for mingle in C-INTERCAL; C-INTERCAL uses the rather
confusing method of interpreting a yen character as exclusive-or if
input in Latin-1 but as mingle if input in UTF-8.  (This usually does
the right thing, because CLC-INTERCAL doesn't support UTF-8.)  In the
same way, CLC-INTERCAL has a C-INTERCAL compatibility option to allow
the use of `?' for exclusive-or.

The operators take each pair of consecutive bits in their arguments
(that is, the least significant with the second least significant, the
second least significant with the third least significant, the third
least significant with the fourth least significant, and so on, with the
pair consisting of the most significant and least significant being used
to calculate the most significant bit of the result), and perform an
appropriate logic operation on them; and sets a bit of the result if and
only if both bits in the pair were set, or sets each bit corresponding
to each pair where either bit was set, and exclusive or sets if and
only if the bits in the pair had different values (that is, one was
set, but not both).  So for instance, `#&26' is 16 (26 is 1A in
hexadecimal or 11010 in binary); `#V26' is 31 (11111 in binary), and
`#?26' is 23 (10111 in binary).

The most commonly seen use for these operators is to carry out bitwise
ands, ors, and exclusive ors between two different 16-bit expressions,
by mingling them together, applying a unary binary logic operator, and
selecting every second bit of the result; such code often results due to
people thinking in terms of some other language when writing INTERCAL,
but is still often useful.  (Historically, the first idiom added to the
optimizer, apart from constant folding, was the mingle/unary/select
sequence.)  There are more imaginative uses; one impressive example is
the exclusive or in the test for greater-than from the original
INTERCAL-72 system library:

     DO :5 <- "'?":1~'#65535$#0'"$":2~'#65535$#0'"'
          ~'#0$#65535'"$"'?":1~'#0$#65535'"$":2~'#0$
          #65535'"'~'#0$#65535'"
     DO .5 <- '?"'&"':2~:5'~'"'?"'?":5~:5"~"#65535~
          #65535"'~'#65535$#0'"$#32768'~'#0$#65535'"
          $"'?":5~:5"~"#65535$#65535"'~'#0$#65535'"'
          "$"':5~:5'~#1"'~#1"$#2'~#3

The first statement works out the value of :1 bitwise exclusive or :2;
the second statement then works out whether the most significant set bit
in :5 (that is, the most significant bit that differs between :1 and :2)
corresponds to a set bit in :2 or not.  In case that's a bit too
confusing to read, here's the corresponding optimizer idiom (in OIL):

     ((_1~:2)~((?32(:2~:2))^#2147483648))->(_1>(:2^_1))

(Here, the ^ refers to a bitwise exclusive or, an operation found in OIL
but not in INTERCAL, which is why the INTERCAL version is so much
longer.)  The INTERCAL version also has some extra code to check for
equality and to produce 1 or 2 as the output rather than 0 or 1.


File: ick.info,  Node: Array Subscript,  Prev: Unary Binary Logic,  Up: Operators

6.3.4 Array Subscript
---------------------

INTERCAL-72       C-INTERCAL        CLC-INTERCAL      J-INTERCAL
------------------------------------------------------------------------ 
yes               version 0.7+      all versions      all versions

In order to access the elements of an array, either to read or write
the array, it is necessary to use the array subscript operator `SUB'.
Note that an array element is not a variable, so it is not accepted as
an acceptable argument to statements like `IGNORE'; however, it can be
assigned to.

The syntax for an array element is the array, followed by the keyword
`SUB', followed by an expression for the element number in the array.
In the case of a multidimensional array, more than one expression is
given after the keyword `SUB' to give the location of the element in
each of the array's dimensions.  The first element in an array or array
dimension is numbered 1.

For instance, this is a legal (but not particularly useful) INTERCAL
program with no syntax errors that shows some of the syntaxes possible
with array subscripting:

     PLEASE ,1 <- #2
     DO .1 <- #2
     DO ,1 SUB .1 <- #1
     DO ,1 SUB #1 <- ,1 SUB #2
     PLEASE ;1 <- #2 BY #2
     DO ;1 SUB #1 #2 <- ,1 SUB ,1 SUB .1
     DO READ OUT ;1SUB#1.1
     DO GIVE UP

Grouping can get complicated when nested array subscripting is used,
particularly with multiple subscripts.  It is the programmer's job to
write an unambiguous statement, and also obey the extra grouping rules
that apply to array subscripts; see *Note Grouping Rules::.


File: ick.info,  Node: Statements,  Next: System Library,  Prev: Expressions,  Up: Top

7 Statements
************

There is a wide range of statements available to INTERCAL programs;
some identifiably belong to a particular variant or dialect (such as
Backtracking INTERCAL), but others can be considered to be part of the
'core language'.  The statements listed here are those that the
C-INTERCAL compiler will accept with no compiler switches to turn on
particular dialect options.  Note that many statements have slightly
different effects in different implementations of INTERCAL; known
incompatibilities are listed here, but it's important to check your
program on multiple compilers when attempting to write a portable
program.

* Menu:

* Syntax Error::              Why use a deliberate syntax error?
* Calculate::                 Assigning to variables and arrays
* NEXT FORGET and RESUME::    INTERCAL-72-style flow control
* STASH and RETRIEVE::        Value stacks and scoping
* IGNORE and REMEMBER::       Creating read-only variables
* ABSTAIN and REINSTATE::     Dynamic DOs and DON'Ts
* READ OUT and WRITE IN::     INTERCAL input and output
* GIVE UP::                   How to end a program
* TRY AGAIN::                 Control flow without loops
* COME FROM and NEXT FROM::   Time-reversed GOTO


File: ick.info,  Node: Syntax Error,  Next: Calculate,  Up: Statements

7.1 Syntax Error
================

INTERCAL-72       C-INTERCAL        CLC-INTERCAL      J-INTERCAL
------------------------------------------------------------------------ 
yes               version 0.15+     all versions      all versions

One of the more commonly-used commands in INTERCAL is the syntax error.
A properly-written syntax error looks nothing like any known INTERCAL
command; a syntax error that looks vaguely like a command but isn't may
confuse C-INTERCAL before version 0.28, and possibly other compilers,
into bailing out at compile time in some situations (this is known as a
`serious syntax error'), and so is not portable.  For other syntax
errors, though, the semantics are easily explained: there is a run-time
error whenever the syntax error is actually executed, and the line
containing the syntax error is used as the error message.

One purpose of this is to allow your programs to produce their own
custom errors at run time; however, it's very important to make sure
that they start and end in the right place, by manipulating where
statement identifiers appear.  Here's a correct example from the system
library:

     DOUBLE OR SINGLE PRECISION ARITHMETIC OVERFLOW

This is a valid INTERCAL command, that produces an error when run (note
the `DO' at the start).  An even more common use is to produce an
initially abstained syntax error by using an appropriate statement
identifier, for instance

     PLEASE NOTE THAT THIS IS A COMMENT

This would produce an error if reinstated somehow, but assuming that
this isn't done, this is a line of code that does nothing, which is
therefore equivalent to a comment in other programming languages.  (The
initial abstention is achieved with the statement identifier `PLEASE
NOT'; the extra `E' causes the command to be a syntax error, and this
particular construction is idiomatic.)

Referring to the set of all syntax errors in a program (or the set of
all commands of any other given type) is achieved with a special
keyword known as a `gerund'; gerund support for syntax errors is
resonably recent, and only exists in CLC-INTERCAL (version 1.-94.-3 and
later, with `COMMENT', `COMMENTS', or `COMMENTING'), and C-INTERCAL
(`COMMENT' in version 0.26 and later, and also `COMMENTS' and
`COMMENTING' in version 0.27 and later).  Therefore, it is not portable
to refer to the set of all syntax errors by gerund; using a line label
is a more portable way to refer to an individual syntax-error command.


File: ick.info,  Node: Calculate,  Next: NEXT FORGET and RESUME,  Prev: Syntax Error,  Up: Statements

7.2 Calculate
=============

INTERCAL-72       C-INTERCAL        CLC-INTERCAL      J-INTERCAL
------------------------------------------------------------------------ 
yes               all versions      all versions      all versions

At present, the only INTERCAL command that contains no keywords (apart
from the statement identifier and possibly `ONCE' or `AGAIN') is what
is known as the `calculate' command.  It is used to assign values to
variables, array elements, and arrays; assigning a value to an array
changes the number of elements that that array can hold, and causes the
values of all elements previously in that array to be lost.  The syntax
of a calculate command is as follows:

     DO .1 <- ':2~:3'~#55

That is, the command is written as a variable or array element, then
the `<-' operator (known as an `angle-worm' and pronounced `gets'),
then an expression to assign to it.  In the special case when an array
is being dimensioned by assigning a value to it, the expression can
contain the keyword `BY' to cause the array to become multidimensional;
so for a 3 by 4 by 5 array, it would be possible to write

     DO ,1 <- #3 BY #4 BY #5

The calculate command always evaluates the expression, even if for some
reason the assignment can't be done (for instance, if the variable
being assigned to is read-only); this is important if the expression
has side-effects (for instance, giving an overflow error).  If the
variable does happen to be read-only, there is not an error; the
expression being assigned to it is just evaluated, with the resulting
value being discarded.

The gerund to refer to calculations is `CALCULATING'; however, if you
are planning to use this, note that a bug in older versions of
C-INTERCAL means that assignments to arrays are not affected by this
gerund before version 0.27.

CLC-INTERCAL from 1.-94.-4 onwards, and C-INTERCAL from 0.26 onwards,
allow arbitrary expressions on the left hand side of an assignment
(C-INTERCAL only if the `-v' option is used); for more information on
how such `reverse assignments' work, see *Note Operand Overloading::.


File: ick.info,  Node: NEXT FORGET and RESUME,  Next: STASH and RETRIEVE,  Prev: Calculate,  Up: Statements

7.3 NEXT, FORGET and RESUME
===========================

INTERCAL-72       C-INTERCAL        CLC-INTERCAL      J-INTERCAL
------------------------------------------------------------------------ 
yes               all versions      see text          all versions

The only flow-control commands in INTERCAL-72 were `NEXT', `RESUME',
and `FORGET'; together these manipulate a stack of locations in the
program known as the `NEXT stack'.  Although all INTERCAL compilers
have implemented these, from CLC-INTERCAL version 0.05 onwards
CLC-INTERCAL has considered them obsolete, and therefore a special
command-line switch needs to be used to enable them.  (They are still
the most portable flow-control commands currently available, though,
precisely because INTERCAL-72 implements nothing else.)  Note that there
is a strict limit of 80 locations on the NEXT stack, enforced by all
known INTERCAL compilers; this helps to enforce good programming style,
by discouraging NEXT-stack leaks (which are otherwise quite easy to
write).

Here are examples to show the syntax of these three statements:

     DO (1000) NEXT
     DO FORGET '.1~.1'~#1
     DO RESUME .5

The `NEXT' command takes a line label as its argument (unlike most
other INTERCAL commands, it comes after its argument rather than
before); both `FORGET' and `RESUME' take expressions.  (CLC-INTERCAL
from version 0.05 onwards also allows an expression in `NEXT', rather
than a label, to give a computed `NEXT', but this behaviour was not
implemented in other compilers, and is deprecated in CLC-INTERCAL along
with noncomputed `NEXT'; if computed `NEXT' is ever implemented in
C-INTERCAL, it will likely likewise be deprecated upon introduction).
(Update: it was implemented in C-INTERCAL version 0.28, but only as
part of the external calls system, so it cannot be used in ordinary
programs; a sample expansion library gives in-program access to a
limited form of computed `NEXT', but should probably not be used.)
Running a `NEXT' causes the program control to transfer to the command
whose line label is referenced, and also saves the location in the
program immediately after the `NEXT' command on the top of the NEXT
stack.

In order to remove items from the `NEXT' stack, to prevent it filling
up (which is what happens with a naive attempt to use the `NEXT'
command as an equivalent to what some other languages call GOTO), it is
possible to use the `FORGET' or `RESUME' commands.  They each remove a
number of items from the NEXT stack equal to their argument; `RESUME'
also transfers control flow to the last location removed from the
`NEXT' stack this way.  Trying to remove no items, or more items than
there are in the stack, does not cause an error when `FORGET' is used
(no items or all the items are removed respectively); however, both of
these cases are errors in a `RESUME' statement.

Traditionally, boolean values in INTERCAL programs have been stored
using #1 and #2 as the two logic levels.  This is because the easiest
way to implement an if-like construct in INTERCAL-72 is by `NEXTING',
then `NEXTING' again, then `RESUMING' either by 1 or 2 according to an
expression, and then if the expression evaluated to 1 `FORGETTING' the
remaining NEXT stack entry.  By the way, the previous sentence also
explained what the appropriate gerunds are for `NEXT', `RESUME', and
`FORGET'.


File: ick.info,  Node: STASH and RETRIEVE,  Next: IGNORE and REMEMBER,  Prev: NEXT FORGET and RESUME,  Up: Statements

7.4 STASH and RETRIEVE
======================

INTERCAL-72       C-INTERCAL        CLC-INTERCAL      J-INTERCAL
------------------------------------------------------------------------ 
yes               all versions      all versions      all versions

The NEXT stack is not the only stack available in an INTERCAL program;
each variable used in the program also has its own stack, which holds
values of the same type as the variable.  The `STASH' command pushes a
variable's value onto that variable's stack; `RETRIEVE' can be used in
the same way to pop the top element of a variable's stack to replace
that variable's value.  The syntax is the same as most other INTERCAL
commands, with the word `STASH' or `RETRIEVE' followed by the variable
or variables to stash or retrieve:

     DO STASH .1 + ;2
     DO RETRIEVE ,3

Note that it is possible to stash or retrieve multiple variables at
once, by listing their names separated by intersections (`+'); it's
even possible to stash or retrieve a variable twice in the same
statement.

It is not entirely clear how `RETRIEVE' interacts with `IGNORE' in
historical INTERCAL-72 compilers; the three modern INTERCAL compilers
all use different rules for the interaction (and the C-INTERCAL
maintainers recommend that if anyone decides to write their own
compiler, they choose yet another different rule so that looking at the
interaction (the so-called `ignorret test') can be used as a method of
determining which compiler is running):

   * C-INTERCAL treats a retrieval just like an assignment.  That is, a
     read-only variable will not be changed by a retrieval, and will
     remain read-only, but the side-effect of popping that variable's
     stash will still happen.

   * J-INTERCAL ignores the read-only status of a variable when
     retrieving it from a stash; the value of the variable changes
     despite being read-only.  The variable remains read-only; the
     `RETRIEVE' simply allows a change to its value despite the
     read-only status.

   * CLC-INTERCAL is the most complicated; it stores read-only status or
     otherwise in the stash, along with the variable's value.  This
     means that if a variable was stashed when read-only, retrieving it
     will retrieve its value and set it to read-only regardless of its
     previous read-only status; likewise, if a variable was stashed
     when read-write, retrieving it will retrieve its value and set it
     to read-write even if it was previously read-only.


The appropriate gerunds for `STASH' and `RETRIEVE' are `STASHING' and
`RETRIEVING' respectively.


File: ick.info,  Node: IGNORE and REMEMBER,  Next: ABSTAIN and REINSTATE,  Prev: STASH and RETRIEVE,  Up: Statements

7.5 IGNORE and REMEMBER
=======================

INTERCAL-72       C-INTERCAL        CLC-INTERCAL      J-INTERCAL
------------------------------------------------------------------------ 
yes               all versions      all versions      all versions

Variables in INTERCAL can be either read-write or read-only.  At the
start of a program, all variables are read-only, but this status can be
changed dynamically during execution of a program using the `IGNORE'
and `REMEMBER' statements (whose gerunds are `IGNORING' and
`REMEMBERING' respectively).  The syntax is the same as for `STASH' and
`RETRIEVE': the command's name followed by an intersection-separated
list of variables.  For instance:

     DO IGNORE .4
     DO REMEMBER ,4 + ;5

Using the `IGNORE' statement sets a variable to be read-only (or does
nothing if it's read-only already); `REMEMBER' sets it to be
read-write.  Any attempt to assign to a read-only variable silently
fails.  One place that this is used is in the system library; instead
of not assigning to a variable in certain control flow paths, it
instead sets it to be read-only so that subsequent assignments don't
change its value (and sets it to be read-write at the end, which
succeeds even if it was never set read-only in the first place); the
advantage of this is that it doesn't need to remember what flow path
it's on except in the variable's ignorance status.

The interaction between `IGNORE' and `RETRIEVE' was never defined very
clearly, and is in fact different in C-INTERCAL, CLC-INTERCAL and
J-INTERCAL; for more details, see *Note RETRIEVE::.


File: ick.info,  Node: ABSTAIN and REINSTATE,  Next: READ OUT and WRITE IN,  Prev: IGNORE and REMEMBER,  Up: Statements

7.6 ABSTAIN and REINSTATE
=========================

INTERCAL-72       C-INTERCAL        CLC-INTERCAL      J-INTERCAL
------------------------------------------------------------------------ 
yes               all versions      all versions      all versions

The statement identifier of a statement determines whether it's in an
abstained or reinstated state at the start of a program; these states
determine whether the statement runs at all when it's encountered.  It
is, however, possible to change this state dynamically during a
program's execution, and the statements to do this are rather
appropriately named `ABSTAIN' and `REINSTATE'.  There are two forms of
each, one which takes a single line label (which must be constant in
most compilers, but can instead be an expression in recent CLC-INTERCAL
versions), and one which takes an intersection-delimited list of
gerunds.  They look like this:

     DO ABSTAIN FROM ABSTAINING + REINSTATING
     DO ABSTAIN FROM (10)
     DO REINSTATE CALCULATING
     DO REINSTATE (22)

(This also illustrates the gerunds used for these commands; note that
`ABSTAINING' from `REINSTATING' is generally a bad idea!)  The line
referenced, or every command represented by any gerund referenced, are
reinstated or abstained as appropriate (effectively changing the DO to
DON'T (or PLEASE to PLEASE DON'T, etc.), or vice versa).  Using these
forms of `ABSTAIN' and/or `REINSTATE' won't abstain from a command
that's already abstained, or reinstate a command that's already
reinstated.

There is a strange set of restrictions on `ABSTAIN' and `REINSTATE'
that has existed since INTERCAL-72; historically such restrictions have
not always been implemented, or have not been implemented properly.
They together define an unusual interaction of `ABSTAIN' and `GIVE UP'
(note, for instance, that there isn't a gerund for `GIVE UP').  The
wording used in the INTERCAL-72 manual is:

     [...] the statement DO ABSTAIN FROM GIVING UP is not accepted, even
     though DON'T GIVE UP is. [...] DO REINSTATE GIVING UP is invalid,
     and attempting to REINSTATE a GIVE UP statement by line label will
     have no effect.  Note that this insures that DON'T GIVE UP will
     always be a "do-nothing" statement.

This restriction was not implemented at all in the only CLC-INTERCAL
version before 0.02 (i.e. version 0.01), or in C-INTERCAL versions
before 1.26.  The restriction was implemented in C-INTERCAL version 1.26
and CLC-INTERCAL versions 0.02 and later as "`GIVE UP' cannot be
`REINSTATED' or `ABSTAINED FROM'"; however, this is not strictly the
same as the definition used by INTERCAL-72 (C-INTERCAL still uses this
definition in CLC-INTERCAL compatibility mode).  The J-INTERCAL
implementation of this restriction is to make `REINSTATING' or
`ABSTAINING' from a line label that refers to a `GIVE UP' statement a
compile-time error, but this does not fit the INTERCAL-72 definition
either.  The definition adopted with version 0.27 and later of
C-INTERCAL, which is hopefully correct, is to allow abstaining from a
`GIVE UP' statement by line number but to rule out the other three
cases (reinstating by line number silently fails, reinstating or
abstaining by gerund is impossible because there is no gerund).

As well as CLC-INTERCAL's extension to abstain/reinstate by computed
line number, there is also (since version 0.25) a C-INTERCAL-specific
extension to `ABSTAIN', also known as `computed abstain', but with a
different syntax and different semantics.  It's written like an
ordinary `ABSTAIN', but with an expression between the words `ABSTAIN'
and `FROM', for instance:

     DO ABSTAIN #1 FROM (1000)
     DO ABSTAIN .2 FROM WRITING IN

Unlike non-computed `ABSTAIN', this form allows a command to be
abstained from even if it's already been abstained from; so if the
first example command is run and line (1000) is already abstained, it
becomes `double-abstained'.  The number of times the statement is
abstained from is equal to the number of times it was already abstained
from, plus the expression (whereas with non-computed abstain, it ends
up abstained once if it wasn't abstained at all, and otherwise stays at
the same abstention status).  Reinstating a statement always
de-abstains it exactly once; so double-abstaining from a statement, for
instance, means it needs to be reinstated twice before it will actually
execute.

There are many uses for `ABSTAIN' (both the computed and non-computed
versions) and `REINSTATE', especially when interacting with `ONCE' and
`AGAIN' (*note ONCE and AGAIN::); the computed version, in particular,
is a major part of a particular concise way to write conditionals and
certain kinds of loops.  They also play an important role in
multithreaded programs.


File: ick.info,  Node: READ OUT and WRITE IN,  Next: GIVE UP,  Prev: ABSTAIN and REINSTATE,  Up: Statements

7.7 READ OUT and WRITE IN
=========================

The `READ OUT' and `WRITE IN' commands are the output and input
commands in INTERCAL; they allow communication between the program and
its user.  There was a numeric I/O mechanism implemented in
INTERCAL-72, and it (or trivial variants) have been likewise
implemented in all more modern variants.  However, it had some obvious
deficiences (such as not being able to read its own output) which meant
that other methods of I/O were implemented in C-INTERCAL and
CLC-INTERCAL.

The syntax of `READ OUT' and `WRITE IN' is the same in all cases: the
name of the command followed by an intersection-separated list of
items; the form of each item, the compiler you are using, and its
command line arguments together determine what sort of I/O is used,
which can in be different for different elements in the list.

* Menu:

* INTERCAL-72 I/O::        Spelt-out numbers and Roman numerals
* C-INTERCAL I/O::         The Turing Tape I/O system
* CLC-INTERCAL I/O::       Baudot and mingled binary


File: ick.info,  Node: INTERCAL-72 I/O,  Next: C-INTERCAL I/O,  Up: READ OUT and WRITE IN

7.7.1 INTERCAL-72 I/O
---------------------

INTERCAL-72       C-INTERCAL        CLC-INTERCAL      J-INTERCAL
------------------------------------------------------------------------ 
yes               all versions      see text          all versions

INTERCAL-72 had its own versions of I/O commands; these commands are
available in all modern INTERCAL compilers as well (but CLC-INTERCAL
implements output slightly differently).  To distinguish INTERCAL-72
input and output from the other more modern types of I/O, the `READ
OUT' and `WRITE IN' commands must take one of the following values: a
onespot or twospot variable, a single element of a tail or hybrid
array, or (in the case of `READ OUT') a constant, meaning that these
are some examples of the possible forms:

     READ OUT .1
     READ OUT ;2 SUB .3:4
     READ OUT #3
     WRITE IN :4
     WRITE IN ,5 SUB #6

The statements do what you would expect; `READ OUT' outputs its
argument to the user, and `WRITE IN' inputs a number from the user and
assigns it to the variable or array element referenced.  (If the
variable, or the array that contains the array element, happens to be
read-only, the input or output still happens but in the case of `WRITE
IN' silently skips the assignment, instead throwing away the input.)
The formats used for input and output are, however, different from each
other and from the formats used by most mainstream languages.

Input is achieved by writing a number in decimal, one digit at a time,
with each digit written out as a word; so to input the number 12345, a
user would have to type `ONE TWO THREE FOUR FIVE' as input (if they
were using English, the most portable choice of language).  In
INTERCAL-72 only English is accepted as a language, but other compilers
accept other languages in addition.  C-INTERCAL from version 0.10
onwards accepts English, Sanskrit, Basque, Tagalog, Classical Nahuatl,
Georgian, and Kwakiutl; also Volapu"k from version 0.11 onwards, and
Latin from version 0.20 onwards.  J-INTERCAL accepts the same languages,
except with Esperanto instead of Latin; from version 0.05 of
CLC-INTERCAL onwards, the same list of languages as C-INTERCAL is
supported (apart from Latin, which was added in version 1.-94.-8), plus
Scottish Gaelic.

The format that output can be read in is a modified form of Roman
numerals, known as `butchered' Roman numerals.  INTERCAL-72, C-INTERCAL
and J-INTERCAL do this the same way; CLC-INTERCAL is somewhat
different. The characters `I', `V', `X', `L', `C', `D', and `M' mean 1,
5, 10, 50, 100, 500 and 1000 respectively, placing a lower-valued
letter after a higher-valued letter adds them, and placing a
lower-valued letter before a higher-valued letter subtracts it from the
value; so `XI' is 11 and `IX' is 9, for instance.  In INTERCAL-72,
C-INTERCAL, and J-INTERCAL, a bar over a numeral multiplies its value
by 1000, and writing a letter in lowercase multiplies its value by
1000000; however, CLC-INTERCAL uses lowercase to represent
multiplication by 1000 and for multiplication by 1000000 writes a
backslash before the relevant numeral.


File: ick.info,  Node: C-INTERCAL I/O,  Next: CLC-INTERCAL I/O,  Prev: INTERCAL-72 I/O,  Up: READ OUT and WRITE IN

7.7.2 C-INTERCAL I/O
--------------------

INTERCAL-72       C-INTERCAL        CLC-INTERCAL      J-INTERCAL
------------------------------------------------------------------------ 
no                version 0.07+     version 0.05+     no

C-INTERCAL's method of character-based (rather than numeric) input and
output is known as the Turing Tape method; it is a binary
(character-set-agnostic) input/output mechanism.  To specify that
C-INTERCAL-style I/O is being used, an array must be used as the
argument to `READ OUT' or `WRITE IN'; as the syntax is the same as for
CLC-INTERCAL's I/O, command-line arguments and the capabilities of the
version of the compiler being used serve to distinguish the two
mechanisms.

The character-based input writes as many characters into a tail or
hybrid array as will fit, one character in each element.  The number
that's written into the array is not the character code, though, but
the difference between the character code and the previous character
code, modulo 256.  (To be precise, the code is the new character minus
the previous character, or 256 minus (the previous character minus the
new character) if the previous character had a higher character code;
the 'previous character' is the previous character from the input, not
the previous character written into the array.)  End-of-file causes 256
to be written into the array.  The concept is that of a circular tape
containing all the characters, where the program measures how many
spaces it needs to move along the tape to reach the next character.
The 'previous character' starts at 0, but is preserved throughout the
entire program, even from one `WRITE IN' to the next.

Character-based output uses a similar model, but conceptually the
output device moves on the inside of the tape, rather than on the
outside.  Therefore, the character is that is actually output is the
bit-reversal of the difference between the last character output before
it was bit-reversed and the number found in the array (subtracting in
that order, and adding 256 if the result is negative).  (Rather than
trying to parse the previous sentence, you may find it easier to look
either at the source code to the compiler if you have it (the relevant
part is binout in `src/cesspool.c') or at some example C-INTERCAL
programs that do text-based I/O.)


File: ick.info,  Node: CLC-INTERCAL I/O,  Prev: C-INTERCAL I/O,  Up: READ OUT and WRITE IN

7.7.3 CLC-INTERCAL I/O
----------------------

INTERCAL-72       C-INTERCAL        CLC-INTERCAL      J-INTERCAL
------------------------------------------------------------------------ 
no                version 0.27+     all versions      no

There are also two CLC-INTERCAL-specific I/O mechanisms.  These are
Baudot-based text I/O (which is also implemented from C-INTERCAL version
0.27 onwards), and CLC-INTERCAL generalised binary I/O (not implemented
in C-INTERCAL).

Baudot text-based I/O is specified by using a tail array as an argument
to `WRITE IN' or `READ OUT'.  (A tail array can also be used to specify
C-INTERCAL-style Turing Tape I/O.  In order to determine which is used:
both C-INTERCAL and CLC-INTERCAL use their own sort of I/O unless a
command-line argument instructs them to use the other.)  In the case of
`WRITE IN', one line of input is requested from the user (C-INTERCAL
requires this to be input in Latin-1, and will then automatically
convert it; CLC-INTERCAL gives the option of various character sets for
this input as command-line options); the final newline is removed from
this line, then it is converted to extended Baudot and stored in the
tail array specified (causing an error if the array is too small).
Because Baudot is only a 5-bit character set, each element is padded to
16 bits; CLC-INTERCAL pads with zeros, C-INTERCAL pads with random
bits.  Trying to input at end-of-file will act as if the input were a
blank line.  `READ OUT' is the reverse; it interprets the array as
extended Baudot and converts it to an appropriate character set
(Latin-1 for C-INTERCAL, or whatever was specified on the command line
for CLC-INTERCAL), which is output to the user, followed by a newline.
Note that the Baudot is often longer than the corresponding character
in other character sets due to the need to insert shift codes; for
information on the extended Baudot character set, *Note Character
Sets::.

Generalised binary I/O is specified using a hybrid array as an argument
to `WRITE IN' or `READ OUT'.  Input works by reading in a number of
bytes equal to the length of the array (without trying to interpret
them or translating them to a different character set), prepending a
byte with 172 to the start, padding each byte to 16 bits with random
data, then replacing each pair of consecutive bytes (that is, the first
and second, the second and third, the third and fourth, and so on) with
(the first element selected from the second element) mingled with (the
complement of the first element selected from the complement of the
second element).  Output is the exact opposite of this process.
End-of-file reads a 0, which is padded with 0s rather than random data;
if a non-end-of-file 0 comes in from the data, its padding will contain
at least one 1.  Any all-bits-0-even-the-padding being read out will be
skipped.


File: ick.info,  Node: GIVE UP,  Next: TRY AGAIN,  Prev: READ OUT and WRITE IN,  Up: Statements

7.8 GIVE UP
===========

INTERCAL-72       C-INTERCAL        CLC-INTERCAL      J-INTERCAL
------------------------------------------------------------------------ 
yes               all versions      all versions      all versions

The `GIVE UP' command causes the program to end (or, in a multithreaded
program, causes the current thread to end).  It is written simply as
`GIVE UP'.  There is not much else to say about it, except to mention
that it is the only way to end the program without an error unless the
last line of the program is `TRY AGAIN', and that it has an unusual
interaction with `ABSTAIN'; for details of this, see *Note ABSTAIN::.
(Going past the last command in the program is an error.)

There is no gerund for `GIVE UP'; in particular, `GIVING UP' is a
syntax error.


File: ick.info,  Node: TRY AGAIN,  Next: COME FROM and NEXT FROM,  Prev: GIVE UP,  Up: Statements

7.9 TRY AGAIN
=============

INTERCAL-72       C-INTERCAL        CLC-INTERCAL      J-INTERCAL
------------------------------------------------------------------------ 
no                version 0.25+     no                no

The `TRY AGAIN' command is a very simple command with many limitations;
its effect is to place the entire program in a loop.  If it exists, it
must be the very last command in the program (it cannot even be
followed by syntax errors), and it causes execution of the program to
go back to the first command.  If the `TRY AGAIN' command is abstained
or for some other reason doesn't execute when reached, it exits the
program without the error that would usually be caused by going past
the last line of code.

The gerund for `TRY AGAIN' is `TRYING AGAIN'.


File: ick.info,  Node: COME FROM and NEXT FROM,  Prev: TRY AGAIN,  Up: Statements

7.10 COME FROM and NEXT FROM
============================

INTERCAL-72       C-INTERCAL        CLC-INTERCAL      J-INTERCAL
------------------------------------------------------------------------ 
no                see text          see text          see text

The `COME FROM' statement (incidentally also invented in 1972, but not
in connection with INTERCAL) is the main control-flow command in
CLC-INTERCAL (which deprecates `NEXT'), and one of two main control
flow structures in other modern INTERCAL compilers.  It takes either a
label or an expression as its argument; these forms are noncomputed
`COME FROM' and computed `COME FROM'.

Noncomputed `COME FROM' was implemented in version 0.5 of C-INTERCAL,
but did not conform to modern-day semantics until version 0.7; it is
available in every version of CLC-INTERCAL and J-INTERCAL.  Computed
`COME FROM' support is available in every version of CLC-INTERCAL and
in C-INTERCAL from version 0.25 onwards, but not in J-INTERCAL; the
variant `NEXT FROM' of `COME FROM' is available from CLC-INTERCAL
version 1.-94.-8 and C-INTERCAL version 0.26 (both computed and
noncomputed).  C-INTERCAL and CLC-INTERCAL also have a from-gerund form
of `COME FROM' and `NEXT FROM', which was also implemented from
CLC-INTERCAL version 1.-94.-8 and C-INTERCAL version 0.26.

The basic rule of `COME FROM' is that if a `COME FROM' statement
references another statement, whenever that statement is reached,
control flow will be transferred to the `COME FROM' after that
statement finishes executing.  (`NEXT FROM' is identical except that in
addition to the `COME FROM' behaviour, the location immediately after
the statement that was nexted from is saved on the NEXT stack, in much
the same way as if the statement being nexted from was itself a `NEXT'.)

Here are examples of noncomputed, computed, and from-gerund `COME FROM':

     DO COME FROM (10)
     DO COME FROM #2$'.1~#1'
     DO COME FROM COMING FROM

(The last example is an infinite loop.  If it said `DO NEXT FROM
NEXTING FROM', it would not be an infinite loop because the NEXT stack
would overflow and cause an error.  This also establishes the gerunds
used for `COME FROM' and `NEXT FROM'.)

There are some things to be careful with involving `COME FROM' and
`NEXT FROM'.  First, if the statement come from or nexted from happens
to be a `NEXT', the `NEXT' doesn't count as 'finishing executing' until
the NEXT stack entry created by the `NEXT' is `RESUME'd to.  In
particular, this means that if `FORGET' is used to remove the entry, or
a `RESUME' with a large argument resumes a lower entry, the `COME FROM'
doesn't steal execution at all.

Second, you may be wondering what happens if two `COME FROM's or `NEXT
FROM's aim at the same line.  In a non-multithreaded program (whether a
program is multithreaded or not is determined by a compiler option for
those compilers that support it), this is an error; but it is only an
error if the statement that they both point to finishes running, and
both `COME FROM's or `NEXT FROM's try to execute as a result (they
might not if, for instance, one is abstained or has a double-oh-seven
causing it not to run some of the time).  If both `COME FROM's or `NEXT
FROM's are noncomputed, however, a compiler can (but does not have to)
give a compile time error if two `COME FROM's or `NEXT FROM's share a
label, and so that situation should be avoided in portable code.  (If
it is wanted, one solution that works for C-INTERCAL and CLC-INTERCAL is
to use computed `COME FROM's or `NEXT FROM's with a constant
expression.)


File: ick.info,  Node: System Library,  Next: TriINTERCAL,  Prev: Statements,  Up: Top

8 System Library
****************

INTERCAL-72       C-INTERCAL        CLC-INTERCAL      J-INTERCAL
------------------------------------------------------------------------ 
yes               all versions      no                all versions

INTERCAL has a system library, called `syslib'.  It is included
automatically at the end of your program by the compiler whenever your
program refers to a line from (1000) to (1999) without defining any
line in that range in the program.  (Although it is not added
automatically by the compiler in CLC-INTERCAL, it is trivial to
concatenate a copy onto the end of the program.)

The intention of the system library is to provide a range of useful
capabilities, like multiplication, that can otherwise be hard to write
in INTERCAL.  System library routines are used by `NEXTING' to their
line number (*note NEXT::), where they will make changes to certain
variables depending on certain other variables (depending on which
routine is called), and `RESUME' back to the original program.  As the
system library is itself written in INTERCAL, there are some
restrictions that need to be obeyed for calls to it to be guaranteed to
work; none of the variables it uses (`.1' to `.6' and `:1' to `:5')
should be read-only or overloaded (although the value of any variables
that aren't mentioned in the routine's description will be preserved by
the routine), and none of the lines in it should have their abstention
status changed by lines outside it (this can happen with blatant
infractions like `DO ABSTAIN FROM (1500)' or more subtle problems like
gerund-abstention) or have `COME FROM's or `NEXT FROM's aiming at them.

The system library is currently available in all bases from 2 to 7
(*note TriINTERCAL::), but not every command is available in every
base, and C-INTERCAL is the only one of the three compilers listed above
that use the system library to ship with a version in bases other than
2.  (This table was originally based on the INTERCAL-72 manual, but has
had extra information added for bases other than 2.) Here, "overflow
checked" means that #1 is assigned to .4 if there is not an overflow,
and #2 is assigned to .4 if there is; "overflow captured" means that if
there is overflow, the digit that overflowed is stored in the variable
referenced.  In all cases, division by 0 returns 0.

Line    Description                                        Bases
----------------------------------------------------------------------- 
(1000)   .3 <- .1 plus .2, error exit on overflow          2, 3, 4,
                                                           5, 6, 7
(1009)   .3 <- .1 plus .2, overflow checked                2, 3, 4,
                                                           5, 6, 7
(1010)   .3 <- .1 minus .2, no action on overflow          2, 3, 4,
                                                           5, 6, 7
(1020)   .1 <- .1 plus #1, no action on overflow           2, 3, 4,
                                                           5, 6, 7
(1030)   .3 <- .1 times .2, error exit on overflow         2, 3, 4,
                                                           5, 6, 7
(1039)   .3 <- .1 times .2, overflow checked               2, 3, 4,
                                                           5, 6, 7
(1040)   .3 <- .1 divided by .2                            2, 3, 4,
                                                           5, 6, 7
(1050)   .2 <- :1 divided by .1, error exit on overflow    2, 3, 4,
                                                           5, 6, 7
(1200)   .2 <- .1 times #2, overflow captured in .3        4, 6
(1210)   .2 <- .1 divided by #2, one digit after the       4, 6
        quartic or sextic point stored in .3               
(1500)   :3 <- :1 plus :2, error exit on overflow          2, 3, 4,
                                                           5, 6, 7
(1509)   :3 <- :1 plus :2, overflow checked                2, 3, 4,
                                                           5, 6, 7
(1510)   :3 <- :1 minus :2, no action on overflow          2, 3, 4,
                                                           5, 6, 7
(1520)   :1 <- .1 concatenated with .2                     2, 3, 4,
                                                           5, 6, 7
(1530)   :1 <- .1 times .2                                 2, 3, 4,
                                                           5, 6, 7
(1540)   :3 <- :1 times :2, error exit on overflow         2, 3, 4,
                                                           5, 6, 7
(1549)   :3 <- :1 times :2, overflow checked               2, 3, 4,
                                                           5, 6, 7
(1550)   :3 <- :1 divided by :2                            2, 3, 4,
                                                           5, 6, 7
(1700)   :2 <- :1 times #2, overflow captured in .1        4, 6
(1710)   :2 <- :1 divided by #2, one digit after the       4, 6
        quartic or sextic point stored in .1               
(1720)   :2 <- :1 times the least significant digit of     5, 7
        .1, overflow captured in .2                        
(1900)   .1 <- uniform random number from #0 to #65535     2, 3, 4,
                                                           5, 6, 7
(1910)   .2 <- normal random number from #0 to .1, with    2, 3, 4,
        standard deviation .1 divided by #12               5, 6, 7

If you happen to be using base 2, and are either using the external
call system (*note External Calls::) or are willing to use it, it is
possible to use a version of the system library written in C for speed,
rather than the default version (which is written in INTERCAL).  To do
this, use the command line options `-eE' (before the INTERCAL file),
and `syslibc' (at the end of the command line).


File: ick.info,  Node: TriINTERCAL,  Next: Multithreading and Backtracking,  Prev: System Library,  Up: Top

9 TriINTERCAL
*************

INTERCAL-72       C-INTERCAL        CLC-INTERCAL      J-INTERCAL
------------------------------------------------------------------------ 
no                version 0.7+      version           no
                                    1.-94.-8+         

One extension to INTERCAL that is implemented by both C-INTERCAL and
CLC-INTERCAL is known as TriINTERCAL, and extends INTERCAL to bases
other than binary.  Unlike ordinary INTERCAL programs, which have the
extension `.i', TriINTERCAL programs in bases from 3 to 7 (the only
allowed bases) have extensions from `.3i' to `.7i' respectively.

The change of numeric base only affects expressions, and in particular
the behaviour of operators, and the range of variables.  (The onespot
and twospot ranges become the highest number of trits or other digits
in the base required that fit inside the binary ranges, so for
instance, the maximum value of a onespot variable in ternary is 59048,
or 3 to the power 10 minus 1.) Interleave/mingle is the simplest to
explain; it alternates digits just as it alternated bits in binary.
The other operators all change, as follows:

   * Exclusive-or becomes two operators, known either as
     subtract-without-borrow and add-without-carry due to their
     mathematical interpretations, or what and sharkfin after their
     Atari syntax representations (`?' and `^').  (In Princeton syntax,
     these are the bookworm or yen sign, and a spike (`|').)  The two
     operators do the same thing in binary, but differ in higher bases.
     (Nevertheless, it is an error to use a sharkfin in binary, because
     it is a so-called `controlled unary operator', as are the rest of
     the new operators defined in this section, which has a lower limit
     on which base it is allowed in.)  Instead of doing the exclusive-or
     operation, the bits being combined are either subtracted or added;
     if the result is out of range for the base being used, the base is
     added or subtracted from the result until it is in range.  (For the
     subtraction, the bit that was less significant is subtracted from
     the bit that was more significant in any given pair of bits,
     except for the subtraction between the most and least significant
     bits, where the most significant bit is subtracted from the least.)

   * The AND and OR operators are generalised into an entire sequence of
     operators; the number of operators available is the same as the
     base that is being used.  In base 3, the third operator is known
     as BUT; in other bases, there are no commonly accepted names for
     the extra operators, so names that reflect the notation are used
     here.

     The way to think of it is this: in base 2, an AND gives the result
     0 if either argument is a 0, and otherwise a 1, and likewise, an OR
     gives the result 1 if either argument is a 1, and otherwise a 0;
     they could be said to favour 0 over 1 and 1 over 0 respectively.
     In base 3, AND favours 0 over 2 over 1, OR favours 2 over 1 over
     0, and BUT favours 1 over 0 over 2.  (The symbol for BUT is `@' (a
     `whirlpool', which is another name for the BUT operation) in Atari
     syntax, and `?' in Princeton syntax.)  The pattern continues: in
     base 4, AND favours 0 over 3 over 2 over 1, BUT favours 1 over 0
     over 3 over 2, 2BUT (written `2@' or `2?') favours 2 over 1 over 0
     over 3, and OR favours 3 over 2 over 1 over 0.  (This can be
     extended to higher bases following the same pattern, introducing
     operators `3@' or `3?', etc., to favour 3, etc., when neither AND
     (which always favours 0) nor OR (which favours the highest digit
     in the base) are available.)  All the whirlpool operators are
     controlled unary operators, which are only legal when both the base
     contains the favoured digit, and they aren't redundant to AND nor
     OR.

   * Select has its semantics modified to deal with more than one
     nonzero digit in the base.  It starts off by doing an OR (in
     whatever base is being used) between the two numbers being
     selected; then the bits of the result are sorted by the bits of
     the right-hand argument to the select, with bits corresponding to
     0s in the right-hand argument ending up more significant than bits
     corresponding to high digits in the right-hand argument.  In base
     2, this has the same effect as a traditional-style select.


Note that the base doesn't affect anything other than variable ranges
and expressions; in particular, it doesn't affect the bit-reversal used
by Turing Tape I/O.  (The tape still has characters written on it in
binary, even though the program uses a different base.)


File: ick.info,  Node: Multithreading and Backtracking,  Next: Operand Overloading,  Prev: TriINTERCAL,  Up: Top

10 Multithreading and Backtracking
**********************************

The multithreading and backtracking extensions to INTERCAL were
originally invented by Malcom Ryan, who implemented `COME FROM'-based
multithreading as a modified version of C-INTERCAL, known as Threaded
INTERCAL, but did not implement backtracking.  (The same functionality
is implemented in C-INTERCAL today, but with different code.  Most
likely, this means that the original code was better.)  He also
invented the original version of Backtracking INTERCAL, but did not
implement it; the only known implementation is the C-INTERCAL one.  A
different version of multithreading, using `WHILE', was implemented as
part of CLC-INTERCAL (like all extensions first available in
CLC-INTERCAL, it is most likely due to Claudio Calvelli) and then added
to C-INTERCAL, although its implications were not noticed for some time
afterwards.

So nowadays, three freely-mixable threading-like extensions to INTERCAL
exist, all of which are implemented in C-INTERCAL.  (A fourth, Quantum
INTERCAL, is implemented in CLC-INTERCAL but not C-INTERCAL, and so
will not be discussed further here.)  If you're wondering about the
description of backtracking as a threading-like extension, it's
implemented with much of the same code as multithreading in C-INTERCAL,
because the INTERCAL version can be seen as roughly equivalent to
multithreading where the threads run one after another rather than
simultaneously.  (This conceptualisation is probably more confusing
than useful, though, and is also not strictly correct.  The same could
probably be said about INTERCAL as a whole, for that matter.)

* Menu:

* Multithreading using COME FROM::  Creating separate threads.
* Multithreading using WHILE::      Creating connected threads.
* Backtracking::                    Multithreading in series, not parallel.


File: ick.info,  Node: Multithreading using COME FROM,  Next: Multithreading using WHILE,  Up: Multithreading and Backtracking

10.1 Multithreading using COME FROM
===================================

INTERCAL-72       C-INTERCAL        CLC-INTERCAL      J-INTERCAL
------------------------------------------------------------------------ 
no                version 0.25+     version 0.05+     no

The original multithreading implementation worked by giving a new
meaning to what was previously an error condition.  If in a
multithreaded program (a program is marked as multithreaded using
options to a compiler) two or more `COME FROM's or `NEXT FROM's (or a
mixture of the two) attempt to steal control simultaneously, the
original thread splits into multiple threads, one for each of the
commands trying to take control, and a different command gains control
of the program in each case.

From then on, all the threads run simultaneously.  The only thing
shared between threads (apart from the environment in which they run)
is the abstained/reinstated status of each command; everything else is
separate.  This means, for instance, that it's possible to change the
value of a variable in one thread, and it will not affect the
corresponding variable in other threads created this way.  Likewise,
there is a separate NEXT stack in each thread; if both a `COME FROM'
and a `NEXT FROM' aim at the same line, for instance, the `NEXT FROM'
thread will end up with a NEXT stack entry that isn't in the `COME
FROM' thread, created by the `NEXT FROM' itself.  This is known as
unwoven thread creation; none of the threads created this way are
`woven' with any of the other threads created this way.  (Whether
threads are woven depends on how they were created.)  If the thread
being split was itself woven with other threads, exactly one of the
resulting threads after the split is woven with the threads that the
original thread was woven to, but the rest will not be woven to
anything.  (If that seems a somewhat unusual rule: well, this is
INTERCAL.)

In C-INTERCAL, there are other guarantees that can be made about unwoven
threads (that is, threads not woven to any other thread).  In
particular, they can all be guaranteed to run at approximately the same
speed; to be more precise, the number of commands that have been given
the chance to execute in any given thread will not differ by more than
2 from the number of commands that have been given the chance to
execute in any other thread that was created at the same time.
(However, `COME FROM's and `NEXT FROM's can make this relationship less
precise; it is unspecified (in the technical sense that means the
compiler can choose any option it likes and change its mind on a whim
without telling anyone) whether a `COME FROM' or `NEXT FROM' aiming at
the current command counts towards the command total or not, thus
causing the relationship to become weaker the more of them have the
chance to execute.  In versions of C-INTERCAL from 0.27 onwards, there
is a third guarantee; that if a `COME FROM' comes from itself, it will
actually give other threads at least some chance to run, at some speed,
by counting itself as a command every now and then; previously this
requirement didn't exist, meaning that a `COME FROM' could block all
threads if it aimed for itself due to the speed restrictions and the
fact that `COME FROM's need not count towards the total command count.)
Also, all commands, including any `ONCE' or `AGAIN' attached to the
command, are atomic; this means that it's impossible for another thread
to conflict with what the command is doing.  (In a departure from the
usual INTERCAL status quo, these guarantees are somewhat _better_ than
in most other languages that implement threading, amusingly continuing
to leave INTERCAL with the status of being unlike any other mainstream
language.)

The only way to communicate between unwoven threads is by changing the
abstention status of commands; this always affects all threads in the
program, whether woven or not.  (The combination of `ABSTAIN' and
`ONCE' is one way to communicate atomically, due to the atomic nature
of `ONCE'.)

If there are at least two threads, the `GIVE UP' command ends the
current thread, rather than the current program.


File: ick.info,  Node: Multithreading using WHILE,  Next: Backtracking,  Prev: Multithreading using COME FROM,  Up: Multithreading and Backtracking

10.2 Multithreading using WHILE
===============================

INTERCAL-72       C-INTERCAL        CLC-INTERCAL      J-INTERCAL
------------------------------------------------------------------------ 
no                version 0.27+     version 0.05+     no

The `WHILE' command (which is not strictly speaking a command, but more
a sort of metacommand that joins commands) is a second method of
achieving multithreading.  (In CLC-INTERCAL, there are at least two
other meanings for `WHILE', but only the one implemented in C-INTERCAL
is discussed here.)  The syntax is somewhat unusual, and consists of
two commands separated by the `WHILE' keyword, but sharing the
statement identifier, execution chance, and any `ONCE'/`AGAIN' keyword
that may be present.  For instance:

     (1) DO COME FROM ".2~.2"~#1 WHILE :1 <-
           "'?.1$.2'~'"':1/.1$.2'~#0"$#65535'"$
           "'"'&.1$.2'~'#0$#65535'"$#0'~#32767$#1"

(OK, maybe that's an unnecessarily complicated example, and maybe it
shouldn't have included the `/' operator which is part of another
INTERCAL extension (*note Operand Overloading::).  Still, I thought
that maybe you'd want to see how addition can be implemented in
INTERCAL.)

A `WHILE' command starts two threads (the original thread that ran that
command and a new one), one of which runs the command to the left of
the `WHILE' and one of which runs the command to the right.  Any line
number applies to the left-hand command, not the WHILE as a whole,
which is a metalanguage construct.  `NEXTING FROM', `ABSTAINING FROM'
or similar behaviour with respect to the `WHILE' itself is impossible,
although it's certainly possible to abstain from either of its operands
(and abstaining from the left operand has much the same effect as
abstaining from the `WHILE' itself; the right-hand thread deliberately
takes a bit of time to get started just so that this behaviour
happens).  The right-command thread starts just before the left command
is run (so `NEXTING', etc., directly to the left command will not start
that loop in the first place); if that command finishes (which may be
almost immediately for something like a calculate command, or take a
long time for something like `NEXT'), that thread loops and reruns that
command as long as the left command has not finished; `COMING FROM'
that command, or a `NEXT'/`NEXT FROM' from/aiming at that command,
doesn't count as finishing that command until it is `RESUME'd back to
(if possible; if it's come from, that command can never end and the
right-hand loop will continue forever, or until it `GIVE's `UP' or the
loop ends due to the command ending later in another thread).  A
`WHILE' command itself exists across all threads of a multithreaded
program in a way; for each left-hand command that ends (in any thread),
the next time a right-hand command ends it will cause the thread it's
looping in to end, regardless of whether that thread corresponds to the
thread in which the left-hand command ended.  (As well as a right-hand
command ending, there's also the possibility that it never got started;
there is a delay before the right-hand command runs during which a
left-hand command ending can prevent the right-hand thread starting in
the first place; this counts as the same sort of event as terminating a
right-hand loop, and can substitute for it anywhere a right-hand
command ending is mentioned.)  There is one exception, in that if two
or more left-hand commands end in a space of time in which no
right-hand commands for that `WHILE' ends, they together only cause one
right-hand command to end.  (What, did you expect the logical and
orthogonal behaviour?)

The two threads produced by a `WHILE' (the original thread and a new
copy of it) have more in common than ordinary INTERCAL threads created
by `COME FROM'; ordinary threads share only `ABSTAIN'/`REINSTATE'
information, whereas the `WHILE'-produced threads count as `woven'
threads which also share variables and stashes.  (They still have
separate instruction pointers, separate instruction pointer stacks,
such as the NEXT stack, and separate choicepoint lists.  Overloading
information is shared, though.)  Being woven is a relationship between
two or more threads, rather than an attribute of a thread, although a
thread can be referred to as being unwoven if it is not woven to any
other thread.

Ordinary multithreading cannot create woven threads. When threads are
created by multiple `COME FROM's from an original thread, which was
woven with at least one other thread, one of the resulting threads
counts as the `original' thread and remains woven; the rest are `new'
threads which initially start out with the same data as the original,
but are not woven with anything.  Backtracking in a thread (*note
Backtracking::) causes it to unweave with any threads it may be woven
with at the time (so the data in the thread that backtracks is set back
to the data it, and the threads it was woven with at the time, had at
the time of the `MAYBE', but the other threads continue with the same
data as before).  The only way to cause three or more threads to become
woven is with a new `WHILE' inside one of the threads that is already
woven, which causes all the new threads to be woven together (the
weaving relationship is transitive).


File: ick.info,  Node: Backtracking,  Prev: Multithreading using WHILE,  Up: Multithreading and Backtracking

10.3 Backtracking
=================

INTERCAL-72       C-INTERCAL        CLC-INTERCAL      J-INTERCAL
------------------------------------------------------------------------ 
no                version 0.25+     no                no

A somewhat unusual threading construct that's available is
backtracking.  In case you haven't come across it before (the concept
exists in other languages but is implemented differently and usually in
a less general way), the basic idea is that instead of executing or not
executing a command, you can `MAYBE' execute a command.  This causes
the command to be executed, but also creates a dormant thread in which
the command wasn't executed; at any time later, the program can either
decide that it liked the consequences of the command and `GO AHEAD' and
get rid of the dormant thread, or decide that it didn't like the
consquences of the command and `GO BACK' to the dormant thread,
discarding the current one.  The dormant thread is more commonly called
a `choicepoint', that is, a point at which a choice was made but a
different choice can still be made, and is generally not thought of as
a thread at all by most programmers.  (In case you're wondering:
dormant threads are always unwoven.)

To create a choicepoint, the statement identifier `MAYBE' is used,
rather than the more usual `DO' or `PLEASE'.  (Combination statement
identifiers are still allowed, but must be in the order `MAYBE PLEASE
DO NOT' with optionally some parts omitted, or different versions of
`NOT' used, or both.) Here's an example:

     MAYBE DON'T GIVE UP

When a command whose statement identifer contains `MAYBE' is reached,
it is executed or not executed as normal, but in addition a choicepoint
is created containing the program as it is at that time.  Only
`ABSTAIN' and `REINSTATE', which always affect all threads in a program
(even choicepoints), can alter the values stored in the choicepoint; so
in this way, a choicepoint is also somewhat similar to the concept of a
continuation in other languages.  The choicepoint is placed on a
choicepoint stack, which is maintained separately for each thread in
much the same way that stashes and the `NEXT' stack are.

The choicepoint does not actually do anything immediately, but if the
program doesn't like the look of where it's ended up, or it decides to
change its mind, or just wants to try all the possibilities, it can
call the `GO BACK' command (which has no arguments, and is just the
statement identifier, optional execution chance, `GO BACK', and
optional `ONCE' or `AGAIN').  This causes the current thread to unweave
from all other threads and then replace itself with the thread created
by the choicepoint on top of the choicepoint stack.  The difference is
that this time, the abstention or reinstatement status of the command
that was modified with `MAYBE' is temporarily reversed for determining
whether it runs or not (this reversal only lasts immediately after the
`GO BACK', and does not affect uses of the command in other threads or
later in the same thread), so unless it has been `ABSTAIN'ed or
`REINSTATE'd in the meantime it will run if and only if it wasn't run
the first time.  The choicepoint stack's top entry is replaced by a
`stale' choicepoint that definitely isn't a thread; attempting to `GO
BACK' to a stale choicepoint instead causes the stale choicepoint to be
deleted and the program to continue executing.  (This is what gives
INTERCAL's backtracking greater flexibility in some ways than some
other languages; to get backtracking without the stale choicepoints
having an effect, simply run `COME FROM' the `GO BACK' as the previous
statement.)

Note that, though, when a thread splits into separate threads (whether
woven or unwoven), the choicepoint stack doesn't split completely, but
remains joined at the old top of stack.  The two choicepoint stacks can
add and remove items independently, but an attempt to `GO BACK' to
before the current thread split off from any other threads that are
still running instead causes the current thread to end, although it
will `GO BACK' as normal if all other threads that split off from it or
that it split off from since the top choicepoint of the stack was
created have ended since.  This means that it's possible to backtrack
past a thread splitting and get the effect of the thread unsplitting,
as long as both resulting threads backtrack; this is another way in
which INTERCAL's backtracking is more flexible than that of some other
languages.

If, on the other hand, a program decides that it likes where it is and
doesn't need to `GO BACK', or it wants to `GO BACK' to a choicepoint
lower down the stack while skipping some of the ones nearer the top of
the stack, it can run the `GO AHEAD' command, which removes the top
choicepoint on the stack, whether it's a genuine choicepoint or just a
stale one.

Both `GO AHEAD' and `GO BACK' cause errors if an attempt is made to use
them when the choicepoint stack is empty.


File: ick.info,  Node: Operand Overloading,  Next: PIC-INTERCAL,  Prev: Multithreading and Backtracking,  Up: Top

11 Operand Overloading
**********************

INTERCAL-72       C-INTERCAL        CLC-INTERCAL      J-INTERCAL
------------------------------------------------------------------------ 
no                version 0.26+     version 0.05+     no

(Operand overloading in C-INTERCAL is nowhere near as advanced as it is
in CLC-INTERCAL.  This chapter only explains the partial implementation
used by C-INTERCAL; for a full implementation, see CLC-INTERCAL and its
documentation.)

Operand overloading is a method of using a onespot or twospot variable
as a substitute for an expression.  When a variable is overloaded to an
expression (which could be another variable, or something more
complex), any uses of that variable cause the expression to be
substituted instead.

At the beginning of the program, all variables stand for themselves; so
`.1' really does mean `.1', for instance.  The meaning of a variable
can be overloaded using the slat operator (`/'), which is the same in
both Princeton and Atari syntax: it is a binary operator whose left
argument must be a onespot or twospot variable and whose right argument
can be any expression.  The slat operator returns the true value of its
left argument, but as a side effect, changes the meaning of its left
argument to be its right argument.  Here is an example:

     DO .1 <- .2/'.3~.4'

The example causes `.2''s true value to be assigned to `.1' (unless of
course `.1' is read-only), but also causes `.2' from then on to
actually mean `'.3~.4'', except when it's the left operand of a slat
operator.  So for instance, `DO .1 <- .2' would actually assign
`'.3~.4'' to `.1'.  Somewhat confusingly, this also works in the other
direction; `DO .2 <- .1' would assign `.1' to `'.3~.4'', which would
have the effect of changing the values of `.3' and `.4' so that
`'.3~.4'' had the correct value, or throw an error if it couldn't
manage this.  (The general rule in this case is that any variable or
constant in the expression that overloads the variable is at risk of
being changed; this is known as a `reverse assignment'.  Code like `DO
.1 <- .1/#1' is entirely capable of changing the value of `#1',
although to protect new INTERCAL users C-INTERCAL will refuse to carry
out operations that change the value of constants unless a command-line
switch (*note -v::) is used to give it permission.  In C-INTERCAL,
changing the value of a constant only changes meshes with that value,
but in CLC-INTERCAL it can also change non-mesh uses of that constant,
so doing so is not portable anyway.)

When multiple overloading rules are in effect, they are all applied;
overloading `.1' to `'.2~.3'' and `.2' to `'.3$.4'' will cause `.1' to
refer to `''.3$.4'~.3''.  However, this expansion stops if this would
cause a loop; to be precise, overloading is not expanded if the
expansion is nested within the same expansion at a higher level (so
`.1/.2' and `.2/.1' together cause `.1' to expand to `.2', which
expands to `.1', which cannot expand any further).  In C-INTERCAL, the
expression on the right hand side of a slat is not evaluated and not
expanded by operand overloading.

`STASHING' a variable causes its overloading information to be stashed
too; `RETRIEVING' it causes its overload rule to also be retrieved from
the stash (or any overload rule on the variable to be removed if there
wasn't one when the variable was stashed).

Overloading a onespot variable to a twospot variable or vice versa is
possible, but the results are unlikely to be predictable, especially if
a onespot variable is used to handle a twospot value.  Possible
outcomes include truncating the value down to the right bitwidth,
throwing an error if a value outside the onespot range is used, and
even temporarily handling the entire twospot value as long as it
doesn't end up eventually being assigned a value greater than twospot.

Note that reverse assignments can cause unpredictable behaviour if an
attempt is made to reverse-assign the same variable twice in the same
expression.  In particular, sequences of commands like `DO .1 <-
.2/'.3$.3' DO .2 <- #6' are liable to succeed assigning garbage to `.3'
rather than failing as they ought to do, and likewise any situation
where a variable is reverse-assigned twice in the same expression may
assign garbage to it.  This behaviour is seen as unsatisfactory,
though, and plans exist to improve it for future versions.


File: ick.info,  Node: PIC-INTERCAL,  Next: CREATE,  Prev: Operand Overloading,  Up: Top

12 PIC-INTERCAL
***************

INTERCAL-72       C-INTERCAL        CLC-INTERCAL      J-INTERCAL
------------------------------------------------------------------------ 
no                version 0.26+     no                no

PIC-INTERCAL is a simplified version of INTERCAL designed especially
for embedded systems, designed to minimise code and data usage by
INTERCAL programs so that they can fit on devices whose memory is
measured in bytes rather than megabytes.  (It is named after the first
microcontroller for which code was successfully generated, and which
influenced the choices of commands, the PIC16F628 manufactured by
Microchip, and is most likely to be portable to other microcontrollers
in the same range.)  C-INTERCAL only compilers as far as C code when
producing PIC-INTERCAL; it is up to the user to find the appropriate
cross-compiler to translate this C into the relevant dialect of machine
code.  (Two header files in the distribution, `src/pick1.h' and
`src/pick2.h', don't have any affect on the compiler but are referenced
by the generated code, and the intent is for the user to change them to
suit the behaviour of the PIC compiler used, because these are not as
standardised as C compilers for everyday systems.)

There are several restrictions on PIC-INTERCAL programs:

   * It's impossible to store more than one item in the STASH for any
     given variable.

   * Many errors are not checked at runtime; it is the programmer's job
     to ensure that runtime errors are avoided.  (The few errors that
     are detected will send the program into an infinite loop, as there
     is no sensible way to exit from a PIC program.)

   * Double-oh-sevens are not randomised, but instead depend merely on
     whether the probability given is greater than 50% or not.

   * The NEXT stack is limited to 16 entries rather than the usual 80.

   * `ABSTAIN' and `REINSTATE' still work, but cannot be computed
     `ABSTAIN's, and will not necessarily work when used to affect the
     system library or calls to it.

   * `READ OUT' and `WRITE IN' don't work.  (See below for a
     replacement.)

   * `COME FROM' and `NEXT FROM' must aim at a label, not an expression
     or gerund.

   * Multithreading and TriINTERCAL cannot be used on PICs.  (Operand
     overloading can be used, but only if your PIC cross-compiler
     supports function pointers; some don't.)


In order to provide I/O capabilities, a new command `PIN' is available.
It controls up to 16 I/O pins on the PIC or other embedded system; an
I/O pin is capable of receiving or sending voltages to an electrical or
electronic circuit.  This explanation assumes that the device being
controlled is a PIC16F628A, and therefore has its pins in two blocks of
8 named `PORTA' and `PORTB'; for other microcontrollers, adapting the
code in `src/pick1.h' is likely to be necessary to tell the compiler
how to control the I/O pins, and the way in which this done will affect
which I/O pins it is that the program will end up being able to
communicate with.

The `PIN' command takes one twospot variable as its argument, like this:

     DO PIN :2

The twospot variable is conceptually divided into 4 blocks of 8 bits.
The highest two blocks control the directions of the pins in `PORTB'
(most significant block) and `PORTA' (second most significant block); a
1 on any bit means that the corresponding I/O pin should be set to send
data, and a 0 means that it should be set to receive data.  The lower
two blocks control the values on the pins that are sending (and are
ignored for receiving pins); the second least significant block
controls `PORTB' and the least significant block controls `PORTA', with
a 1 causing the program to set the output voltage to that of the
microcontroller's negative voltage supply rail, and a 0 causing the
program to set the output voltage to that of the microcontroller's
positive voltage supply rail.  (These voltages may vary on other
systems; consult your system's datasheet and the changes you made to
the header files.)  After setting the pins, the `PIN' command then
reads them as part of the same operation, this time setting the values
of the lower blocks that are receiving, rather than setting the pins
from the lower blocks that are sending.  However, 1 and 0 bits on all
bits of the twospot variable have the opposite meaning when doing this,
so that 1 means receiving/positive voltage rail and 0 means
sending/negative voltage rail.  There is no way to input without
output, or vice versa, but it's trivial to just send the same output
again (which has no effect, because the voltage on sending pins is
maintained at the same level until it is changed), or to ignore the
input received.


File: ick.info,  Node: CREATE,  Next: External Calls,  Prev: PIC-INTERCAL,  Up: Top

13 CREATE
*********

INTERCAL-72       C-INTERCAL        CLC-INTERCAL      J-INTERCAL
------------------------------------------------------------------------ 
no                version 0.28+     see text          no

The `CREATE' command allows the creation of new syntax at runtime.
CLC-INTERCAL has had such a command since 1.-94.-8, but its syntax is
completely different and incompatible with the C-INTERCAL version, and
so is not documented here (see the CLC-INTERCAL documentation for more
details).  The C-INTERCAL version is only defined if the `-a' option is
used on the command line (and a runtime error E000 otherwise), because
it forces the operand overloading code to be introduced and so slows
down every variable access in the program.

The syntax of the `CREATE' command is to write `CREATE', then a line
label, then anything.  OK, well not quite anything; you're restricted
to syntax that is supported by the `just-in-case' compiler that runs on
comments at compile time just in case they gain a meaning later (see
below).  The anything provides an example statement to `CREATE';
statements which look the same (but may differ in details) are created.
Typical syntax for a `CREATE' statement would therefore look something
like this:

     	DO CREATE (5) SWITCH .1 WITH .2

Here, a new `SWITCH WITH' statement (there is no such statement in
INTERCAL normally) is being created.  This command makes it possible to
do this:

             DO SWITCH .3 WITH .4

Normally that line would be an error (E000) due to being unrecognised,
but having been `CREATE'd, it's now a real statement.  (The gerund to
affect created statements is `COMMENT', just like before they were
created; the gerund to affect `CREATE' itself is `CREATION' (`CREATING'
is also allowed, but not as elegant).)  When the created statement is
encountered, it `NEXT's to line (5), the line number specified in the
`CREATE' statement.  In order for the code there to be able to affect
the variables mentioned in the statement, the variables `:1601' (for
the first variable or expression mentioned), `:1602' (for the second
variable or expression mentioned), and so on, are `STASH'ed and then
overloaded to the respective expressions or variables mentioned in the
created command; so `:1601' has been overloaded to mean `.3' and
`:1602' has been overloaded to mean `.4' at this point.  Then, the code
at (5) runs; if it returns via a `RESUME #1', `:1601' and `:1602' will
be `RETRIEVE'd automatically and the program will continue from after
the created statement.  (If you do not resume to that point, say if
you're creating a flow control statement, you'll have to deal with the
stashes for the 1600-range variables yourself.)

So what syntax is available in created statements?  All the capital
letters except `V' (which is an operator in INTERCAL) are available and
can be used freely and as many times as desired; they match themselves
literally.  However, they are not allowed to spell an INTERCAL keyword
at any point (so watch out for `DO' and `FROM', for instance).
Whitespace is allowed, but is ignored (both in the `CREATE' template
statement, and in the code being created; so `DO SW ITCH :8 WITH :50'
will also have been created).  Then, there are three groups of
matchable data: scalar variables (onespot or twospot variables, as used
in the examples above) match other scalar variables, array elements
(like `,4 SUB '.5~.6'') match other array elements, and other
expressions match other other expressions.  Two matchable data may not
appear consecutively in a created command, but must be separated by at
least one capital letter (to prevent array-subscript-related
ambiguities; remember that the just-in-case compiler has to compile
these statements at compile time without knowing what they are).  The
actual expressions used in the `CREATE' statement don't matter; they're
just examples for the runtime to match against.

Some other points: a newer `CREATE' statement supercedes an older
`CREATE' statement if they give equivalent templates, multiple `CREATE'
statements may aim at the same line (this is the recommended technique
for creating a statement that can handle expressions even if they're
array elements or variables; you do this by specifying multiple
templates in multiple `CREATE' statements), and strange things happen
if a twospot variable in the 1600-range is used as an argument to a
created statement itself (because of the stash/retrieve, such a
variable can usually be read, but may not always be able to be written
without the data being lost).


File: ick.info,  Node: External Calls,  Next: Differences to Other Compilers,  Prev: CREATE,  Up: Top

14 External Calls
*****************

INTERCAL-72       C-INTERCAL        CLC-INTERCAL      J-INTERCAL
------------------------------------------------------------------------ 
no                version 0.28+     no                no

C-INTERCAL has a feature allowing INTERCAL and non-INTERCAL code to be
mixed.  This is achieved by causing the non-INTERCAL programs to
participate in the INTERCAL line-numbering model.  The same feature
allows expansion libraries to be linked into the code.

To create a combined program containing INTERCAL and non-INTERCAL code,
use `ick' as the compiler as normal, but specify both the INTERCAL and
non-INTERCAL source files on the command line, and use the `-e'
command-line option.  `ick' will invoke other compilers as necessary,
after modifying the source files accordingly.  At present, external
calls are only supported to and from C.

In each case, it will be the INTERCAL program that is invoked first.
(This means that it is impossible to link together more than one
INTERCAL program, but you probably don't want to, because concatenating
the programs is likely to have a similar effect.)  You can get the
INTERCAL program to `NEXT' to the non-INTERCAL program immediately, or
the non-INTERCAL program to `COME FROM' or `NEXT FROM' the INTERCAL
program immediately, to obtain the effect of running the non-INTERCAL
program first.

Note that external calls are incompatible with PIC-INTERCAL and with
multithreading; note also that you must use `gcc' as your compiler, and
GNU cpp and ld, for them to work in the current version of C-INTERCAL.

* Menu:

* External Calls to C::      How to put INTERCAL calls in C.
* Using External Calls::     What happens when you use -e.
* Expansion Libraries::      Expanding the compiler's capabilities.


File: ick.info,  Node: External Calls to C,  Next: Using External Calls,  Up: External Calls

14.1 External Calls to C
========================

Linking C and INTERCAL programs is acheived by placing various
constructs into the C programs that are equivalent to various INTERCAL
constructs.  It is possible to simulate a line with a label and a dummy
command (which serves as a `COME FROM' suckpoint and `NEXT' target),
`NEXT', `RESUME', and `FORGET', and `COME FROM' and `NEXT FROM'.
Onespot and twospot variables are accessible from inside the C program,
where they can be read and written; however, the INTERCAL program
cannot access any variables inside the C program that weren't part of
the INTERCAL program originally.

To prevent various logical impossibilities, there are restrictions on
where these can be used and what preparation is needed before they are
used.  Also, the semantics are not always exactly what you might expect
for technical reasons.

It should be observed that the INTERCAL link intrudes on the user
namespace.  To prevent possible namespace clashes, no identifiers
starting with `ick_' or `ICK_' should be used anywhere in the linked C
program for any reason, except where specified in this manual.

* Menu:

* External C Call Infrastructure:: Enabling a C program for external calls
* ick_startup::                    Doing things at startup
* ick_linelabel::                  Labelling lines...
* ick_labeledblock::               ...and labelling blocks
* ick_comefrom and ick_nextfrom::  Stealing control from elsewhere
* ick_next::                       The INTERCAL answer to subroutine calls
* ick_resume::                     Going back to before a NEXT
* ick_forget::                     Discarding NEXT stack entries
* ick_get/setone/twospot::         Accessing INTERCAL variables from C
* ick_create::                     CREATE statements via external calls
* External Calls and auto::        Considerations for auto variables


File: ick.info,  Node: External C Call Infrastructure,  Next: ick_startup,  Up: External Calls to C

14.1.1 External C Call Infrastructure
-------------------------------------

For a C program to be connected to an INTERCAL program, it needs to be
marked with the correct header file, and needs to have functions marked
for communication with the INTERCAL program.

`#include <ick_ec.h>'
     The header file `ick_ec.h' must be included using the preprocessor
     in any file which uses any of the INTERCAL external call
     functions, variables, or macros.  (Note that this file may not
     necessarily exist, or exist in the usual place; `ick' will deal
     with making sure the correct header file is included.)  This will
     include `stdint.h' (a standard C header file, which must exist on
     your system), so that you can access INTERCAL variables (the
     INTERCAL types onespot, twospot, tail, hybrid correspond to the C
     types uint16_t, uint32_t, uint16_t*, uint32_t* respectively);
     also, it will provide the prototypes for all the functions and
     definitions for all the macros needed to use the external calls
     system with C.

`ICK_EC_FUNC_START'
`ICK_EC_FUNC_END'
     Many of the INTERCAL interface macros (`ick_linelabel',
     `ick_comefrom', and `ick_nextfrom') make it possible to jump from
     an INTERCAL program to a C program.  Because C doesn't allow
     jumping into the middle of a function, there has to be some way to
     create a block of code which _can_ be jumped into. This is what
     these two macros achieve.

     This declaration and definition:

          ICK_EC_FUNC_START(identifier)
          {
            /* code goes here */
          }
          ICK_EC_FUNC_END

     is equivalent to this:

          void identifier(void)
          {
            /* code goes here */
          }

     except that it is possible to jump from an INTERCAL program into
     the declared and defined program.  (If you need to write a
     prototype for the function early, `void identifier(void);' is
     perfectly acceptable, but an early prototype is not required
     unless you call the function from earlier within the C code.)  Of
     course, you can substitute any identifier that's legal as a
     function name for `identifier' (as long as it doesn't start with
     `ick_' or `ICK_').  The resulting function is a function (for
     instance, you can take its address or call it in the usual ways);
     the only differences are that it can be jumped into from INTERCAL
     code and that it is constrained to take no arguments and return no
     data.  (It can still access global and INTERCAL variables.)  If
     the function is jumped into from INTERCAL code, but then control
     flow reaches the end of the function, or the function `return;'s
     but was not called from C, the resulting behaviour is undefined;
     C-INTERCAL will attempt to continue by some means at that point,
     but may fail.  If a function is unsure whether it gained control
     from C or from INTERCAL code, it may use `ick_return_or_resume'
     (described below).

     Because you are not allowed to declare two C functions with the
     same name (even in different modules), all functions declared with
     `ICK_EC_FUNC_START' must have unique names across the entire
     compilation.



File: ick.info,  Node: ick_startup,  Next: ick_linelabel,  Prev: External C Call Infrastructure,  Up: External Calls to C

14.1.2 ick_startup
------------------

It is sometimes necessary for a C program to do its own initialisation
before the INTERCAL program starts running.  To do so, it can use the
`ick_startup' macro inside a function declared with
`ICK_EC_FUNC_START'; the syntax is `ick_startup(block)', where the
argument is an expression, statement, or compound statement to run.
The argument itself must not contain any ick_-prefixed macros or
functions, may have side effects, and must fit the C preprocessor's
idea of what a macro argument should look like (it's more used to
parsing expressions than blocks; the general rule is to avoid commas
except when they're directly or indirectly inside parentheses or
strings).


File: ick.info,  Node: ick_linelabel,  Next: ick_labeledblock,  Prev: ick_startup,  Up: External Calls to C

14.1.3 ick_linelabel
--------------------

A line label is something that can be `NEXT'ed to and `COME FROM'.
Unlike an INTERCAL line label, it does not label a statement, and
therefore attempts to `ABSTAIN' or `REINSTATE' it may be errors, or may
be ignored (it's unspecified which, which means that either may happen
for any or no reason, but exactly one will happen in any given case,
although the choice might not be consistent).

The macro `ick_linelabel(expression);' may appear anywhere a compound
statement would normally be able to appear.  (That is, it looks like a
function call being used as a standalone expression, but in fact the
places where it can appear are more limited.)  In contrast to ordinary
line labels, an expression can be used rather than just a constant;
however, the behaviour is undefined if the expression has side-effects.
Upon encountering the line label, any `COME FROM's or `NEXT FROM's
aiming at the line label (including `ick_comefrom's and
`ick_nextfrom's) will steal control from the program; `RESUMING' after
a `NEXT FROM' will work, but suffers from the same caveats as
setjmp/longjmp do (any auto variables that change their value between
the `NEXT FROM' and `RESUME' will have their value clobbered (i.e.
their value is no longer reliable and should not be accessed)).  Note
that the INTERCAL variables are immune to this problem.  You can also
avoid the problem by marking variables as `volatile' in the C program.

It is possible to `NEXT' or `ick_next' to a `ick_linelabel', which has
the same effect as saving the `NEXT' stack, calling the function
containing the `ick_linelabel' and then immediately doing a C `goto' to
an imaginary label preceding it.  Due to this possibility, an
`ick_linelabel' is only allowed within a function defined with
`ICK_EC_FUNC_START'.


File: ick.info,  Node: ick_labeledblock,  Next: ick_comefrom and ick_nextfrom,  Prev: ick_linelabel,  Up: External Calls to C

14.1.4 ick_labeledblock
-----------------------

In INTERCAL programs, labels don't stand on their own, but instead
label a statement.  The difference between a standalone line label and
a line label that labels a statement is that `COME FROM's will come
from the _label itself_ (which is before the next statement) when
aiming at a standalone line label, but the _end of the statement_ when
aiming at a labeled statement.  To achieve the same effect in C, the
macro `ick_labeledblock' is available; it can be used as
`ick_labeledblock(expression,expression)' or
`ick_labeledblock(expression,statement)'; the first argument is the
label, and the second argument is an expression or statement to label
(if an expression is labeled, it will be converted to a statement that
evaluates it for its side effects and discards the result).  It is even
permitted to label a block statement in this way.  Note, however, that
you have to contend with the C preprocessor's ideas of where macro
arguments begin and end when doing this.  Other than the position of
the `COME FROM' target created by the label, this behaves the same way
as `ick_linelabel' (so for instance, computed line labels are allowed,
but the expression that computes them must not have side effects, and
it is only allowed within a function defined with `ICK_EC_FUNC_START').


File: ick.info,  Node: ick_comefrom and ick_nextfrom,  Next: ick_next,  Prev: ick_labeledblock,  Up: External Calls to C

14.1.5 ick_comefrom and ick_nextfrom
------------------------------------

The `ick_comefrom' and `ick_nextfrom' macros are, like the other
INTERCAL flow control macros (as opposed to functions), only allowed
within a function defined with `ICK_EC_FUNC_START'.  They act almost
exactly like the INTERCAL statements of the same name (although note
that C statements cannot be `ABSTAIN'ed `FROM' even if they act the
same way as INTERCAL statements); they are written as
`ick_comefrom(expression);' and `ick_nextfrom(expression);'
respectively (note that they must be called as statements, and cannot
be used as part of an expression).  Whenever a standalone line label is
encountered whose expression evaluates to the same number as the
expression inside the `ick_comefrom' or `ick_nextfrom', and that number
is at most 65535, then control will be transferred to the
`ick_comefrom' or `ick_nextfrom', leaving a `NEXT' stack entry behind
in the case of `ick_nextfrom'; likewise, if the end of a labeled
statement, expression or block is reached and the label has the right
number.  Some caveats: the expression need not be constant, but must
not have side effects, must not be negative, and must fit into the
range of an `unsigned long' in the C program (and the statement will do
nothing if the expression evaluates to a value larger than 65535).  In
keeping with the best C traditions, these caveats are not checked, but
instead result in undefined behaviour if breached.

There are also versions `ick_comefromif' and `ick_nextfromif', which
take a second parameter, which is a condition that specifies whether
control is actually stolen from the target.  The condition may have
side effects, and is only run when the line numbers match; it should
return 0 or NULL to leave control flow alone, or nonzero to steal
control, and should be either an integral type or a pointer type.
Although side effects are allowed, the condition must not look at or
alter `auto' or `register' variables in the enclosing function, not
even if they are also marked `volatile'.  (Global and `static'
variables are fine, though.)


File: ick.info,  Node: ick_next,  Next: ick_resume,  Prev: ick_comefrom and ick_nextfrom,  Up: External Calls to C

14.1.6 ick_next
---------------

`ick_next' is a macro that acts like the INTERCAL statement `NEXT'.
Contrary to the other INTERCAL-like macros, it can be used in any
function regardless of whether it was defined with `ICK_EC_FUNC_START';
however, it must still be used as a statement by itself, and a call to
it looks like `ick_next(expression);'.  The expression is the label to
`NEXT' to, and works under the same rules as the expressions for
`ick_comefrom'; it need not be constant (unlike in C-INTERCAL!), but
must not have side effects, must not be negative, must fit into the
range of an unsigned long, and is ignored if it is over 65535.  If
there happen to be multiple labels with the correct value at the time,
the compiler will `NEXT' to one of them.  Bear in mind that there is a
limit of 80 entries to the `NEXT' stack, and that this limit is
enforced.

If the resulting `NEXT' stack entry is `RESUME'd to, the program will
continue after the `ick_next' as if via `setjmp', with all the usual
restrictions that that entails; if the resulting `NEXT' stack entry is
forgotten, then the `ick_next' call will never return.  (Notice the 'as
if via setjmp' condition allows you to preserve the vales of `auto' and
`alloca'-allocated storage as long as its value has not changed since
the `ick_next' was called, which is a significantly more lenient
condition than that normally imposed on such variables (*note External
Calls and auto::).


File: ick.info,  Node: ick_resume,  Next: ick_forget,  Prev: ick_next,  Up: External Calls to C

14.1.7 ick_resume
-----------------

`ick_resume' is a macro, but there are few restrictions on its use; it
is permitted to use it inside an expression (but it returns void,
making this not particularly useful), and acts like a function which
takes an unsigned short argument, returns void, and has a prototype (but
you cannot take its address; if you need to be able to do that, write a
wrapper function for it).  It can be used within any function regardless
of how it was declared, and never returns; instead, it pops the
specified number of `NEXT' stack entries and resumes execution at the
last one popped, just as the INTERCAL statement does.  This causes the
same errors as the INTERCAL statement if the number of entries popped
is zero or larger than the `NEXT' stack.

There is also a macro `ick_return_or_resume();'; it can only be used
inside a function defined with `ICK_EC_FUNC_START', and is equivalent
to `return;' if the function was called from C, or `ick_resume(1);' if
the function was called from INTERCAL.  It's therefore a safe way to
return from such a C function if you don't know how control reached it
in the first place.


File: ick.info,  Node: ick_forget,  Next: ick_get/setone/twospot,  Prev: ick_resume,  Up: External Calls to C

14.1.8 ick_forget
-----------------

The `ick_forget' macro removes `NEXT' stack entries, and the
corresponding C stack entries. It must be called as a statement by
itself, and its invocation looks like this: `ick_forget(expr);', where
the expression is the number of `NEXT' stack entries to forget (all of
them will be forgotten if the number is higher than the number of
entries).  The expression will be casted to an `unsigned short'.

`ick_forget' can only be used inside a function declared with
`ICK_EC_FUNC_START'.  As it is removing stack entries both in INTERCAL
and in C, it will clobber the value of all `auto' variables created
since the highest remaining `NEXT' stack entry came into being (or
since the start of the program, if the `NEXT' stack is emptied by the
command) and also deallocate all `alloca' storage allocated since then.
It also causes the return address of the current function to become
undefined, so that function must not return; control may leave it via
`RESUME', or via `COME FROM', or via `NEXT' or `NEXT FROM' followed by
the relevant `NEXT' stack entry being forgotten (the function is still
'running' but suspended while the `NEXT' stack entry still exists).
(Note that these restrictions are stronger than those on `RESUME'; this
is because `RESUME' preserves most of the stack, but `FORGET' destroys
parts of the stack and therefore cannot avoid destroying the data
stored there.  It could be much worse; a previous (never released)
version of the code didn't remove those parts of the stack in many
circumstances, leading to a stack leak that caused programs to segfault
after a while.)


File: ick.info,  Node: ick_get/setone/twospot,  Next: ick_create,  Prev: ick_forget,  Up: External Calls to C

14.1.9 ick_get/setone/twospot
-----------------------------

This class of four functions make it possible to get and set INTERCAL
scalar variables from C code.  Their prototypes are as follows:

     uint16_t ick_getonespot(unsigned short varnumber);
     void ick_setonespot(unsigned short varnumber, uint16_t newvalue);
     uint32_t ick_gettwospot(unsigned short varnumber);
     void ick_settwospot(unsigned short varnumber, uint32_t newvalue);

The program will error out with a fatal error (*note E200::) if the
variable you request is mentioned nowhere in the INTERCAL program; if
you attempt to set an `IGNORE'd variable, the attempt will silently
fail (just as if you assigned to it in an INTERCAL program).  The get
functions are safe to use in a computed line label, so you can use them
to produce computed line labels that depend on INTERCAL variables.
(`uint16_t' and `uint32_t' are standard C data types; if your system
doesn't provide them, get better system header files.)

If you care about speed, note that .1 is the fastest variable of all to
access, and otherwise variables first mentioned near the top of the
INTERCAL program will be faster to access than variables mentioned
lower down.


File: ick.info,  Node: ick_create,  Next: External Calls and auto,  Prev: ick_get/setone/twospot,  Up: External Calls to C

14.1.10 ick_create
------------------

The `ick_create' function (prototype: `void ick_create(char*, unsigned
long)') allows the external calls system to be used to create new
INTERCAL syntax; to do this, you give a `signature' representing the
syntax you want to define and a line number to the function (which are
its two arguments, respectively).  The signature defines the syntax
that you are defining; whenever that syntax is encountered within the
INTERCAL program, it will `NEXT' to the line number you specify, which
can do various clever things and then `RESUME' back to the INTERCAL
program (or if you're defining a flow-control operation, you might want
to leave the `NEXT' stack entry there and do other things).  However,
note that the overloading of `:1601', etc., will still take place as in
the INTERCAL version of `CREATE' if the `-a' option is used (*note
-a::), so care is needed when writing flow control statements that they
work both with and without the option and don't cause `STASH' leaks
(which means no `FORGET'ting the relevant `NEXT' stack entry, and no
looking at 1600-range variables).  This allows the external calls
system to define whole new INTERCAL commands, with the same power as
any other programming language.

There are various restrictions on what syntax you can `CREATE' with
this method, which are best explained by an explanation of the relevant
C-INTERCAL compiler internals.  When an INTERCAL program is compiled by
C-INTERCAL, any unrecognised statements it comes across are compiled by
a `just-in-case' compiler that attempts to compile them anyway with no
knowledge of their syntax, just in case the syntax becomes defined
later.  (E000 (*note E000::) will be thrown when such statements are
encountered at runtime, unless the syntax has been `CREATE'd since to
give a statement a meaning.)  For the just-in-case compiler to run, the
resulting statement must be completely unrecognised; this means that it
may contain no keywords (not even a sequence of letters that forms a
keyword, such as `FROM' or `DO'), it must consist only of variable
names, expressions, and capital letters other than `V' (because `V' is
a unary operator, so otherwise there would be ambiguity), and in which
any two variable names or expressions are separated by at least one
capital letter.  The compiler will produce a `signature' for the
unknown command that can be defined.

A signature consists of a sequence of characters (and is represented as
a null-terminated string; the runtime makes a shallow copy of the
string and keeps it until the end of the program, so arrangements must
be made to ensure that the storage in which the string is allocated
stays around that long, but this opens up interesting possibilities in
which the signature that was actually `CREATE'd can be modified
retroactively); whitespace is not allowed in a signature.  Capital
letters can be used (apart from `V'), and match the same capital
letters literally in the INTERCAL syntax being created; also available
are the special characters `.,;~', which match respectively a scalar
variable (a onespot or twospot variable such as `:1'), an array
variable (such as `;2'), an array element (such as `,3 SUB #4 #5'), and
an expression that isn't a variable name and isn't an array element
(such as `.4$.5').  If you want to be able to match other things (say,
to be able to match all expressions), you will need to submit multiple
signatures using multiple calls to `ick_create'; maybe you could write
a library to do that automatically.

The routine that is `NEXT'ed to will presumably want to be able to see
what in the INTERCAL program was matched by the signature, so a range
of function-like macros is provided to access that.  They must be run
from within the invocation of the function which was `NEXT'ed into by
the created syntax (*note External Calls and auto:: for when a function
invocation ends, which could be sooner than you think when the
C-INTERCAL external calls system is used), and are undefined behaviour
when that invocation did not gain control from a `CREATE'd statement.
Here are their effective prototypes:

     int ick_c_width(int);
     int ick_c_isarray(int);
     unsigned short ick_c_varnumber(int);
     uint32_t ick_c_value(int);
     /* These require -a to work */
     uint32_t ick_c_getvalue(int);
     void ick_c_setvalue(int, uint32_t);

The first argument to all these macros is the position of the match in
the signature (0 for the first non-capital-letter match in the
signature, 1 for the second, and so on until no more items are left in
the signature to match); specifying a position that isn't in the
signature is undefined behaviour.

`ick_c_width' returns the data type, as a width in bits, of the
expression (or the width in bits of an element of the passed in array),
and `ick_c_isarray' returns 1 if the argument was an array variable or
0 if it was an expression (array elements and scalar variables are
expressions).  `ick_c_varnumber' returns the variable's number (for
instance 123 for `.123'), or 0 if the corresponding argument was not a
variable; in the cases where the argument was a variable, these three
functions together provide enough information to figure out which
variable (which is useful if you're writing an extension which takes a
variable name as an argument).

`ick_c_value' returns the value of the corresponding expression at the
time the `CREATE'd command was called; `ick_c_getvalue' is almost
equivalent, but only works if the `-a' option (*note -a::) was used
during compilation, and returns the value of the corresponding
expression now.  (The uint32_t return type is large enough to hold
either a onespot or twospot value, and will be zero-extended if the
corresponding expression had onespot type.)  `ick_c_setvalue' also
depends on `-a', and will assign to the corresponding expression (be
careful not to provide a value that is too large for it!).  In the case
that the corresponding expression is not a variable, this will attempt
to perform a reverse assignment to the expression, and can produce
ordinary INTERCAL errors if it fails.  It is not possible to
redimension an array this way, as this is assignment, not a calculate
operation.


File: ick.info,  Node: External Calls and auto,  Prev: ick_create,  Up: External Calls to C

14.1.11 External Calls and auto
-------------------------------

Because the external calls system merges the INTERCAL `NEXT' stack with
the C return value and data storage stack (note for pedants: the C
standards nowhere mandate the existence of such a stack, or even mention
one, but the restrictions stated in them imply that implementations have
to act as if such a stack existed, because of the way the scoping rules
and recursion work), the external calls system therefore has severe
effects on data that happens to be stored there.  (In INTERCAL terms,
imagine what would happen if data could be stored on the `NEXT' stack;
if C used the more sensible system of having a `STASH' for each
variable, these problems would never occur in the first place, instead
causing an entirely differnet set of problems.)  Similar considerations
apply to the common nonstandard C extension `alloca', which dynamically
alters the size of the stack; also, in what goes below, `register'
variables should be considered to be `auto', because the compiler may
choose to allocate them on the stack.  Theoretical considerations would
lead one to conclude that variable-length arrays should obey most of
the same restrictions; in practice, though, it's unwise to attempt to
mix those with INTERCAL code at all, except by separating them into
separate functions which aren't flagged with `ICK_EC_FUNC_START' and
use no `ick_'-prefixed identifiers, even indirectly.  (They may cause a
compile to fail completely because they don't mix well with `goto'.)

In the description below, INTERCAL commands should be taken to include
the equivalent C macros.

`NEXT'/`NEXT FROM' paired with `RESUME' have the least effect, and the
most obvious effect, on `auto' variables in the function that was
`NEXT'ed from, which is the same effect that the standard C function
`longjmp' has.  That is, `alloca' storage stays intact, and `auto'
variables have their values `clobbered' (that is, their value is no
longer reliable and should not be used) if they changed since the
corresponding `NEXT' and are not marked as `volatile'.  (This is a very
easy restriction to get around, because changing the values of such
variables is quite difficult without using statically-allocated
pointers to point to them (a dubious practice in any case), and
`volatile' is trivial to add to the declaration.)

`COME FROM' has more restrictions; it deallocates all `alloca' storage
in the function that was `COME FROM', and functions that called it or
that called functions that called it, etc., using C calls (as opposed
to `NEXT'), and those invocations of the functions will cease to exist
(thus destroying any `auto' variables in them), even in the case of
`COMING FROM' a function into the same function.  `auto' variables in
the function that is come into will start uninitialised, even if
initialisers are given in their declaration, and it will be a `new'
invocation of that function.  (It is quite possible that the
uninitialised values in the `auto' variables will happen by chance to
have the values they had in some previous invocation of the function,
though, because they are likely to be stored in much the same region of
memory; but it is highly unwise to rely on this.)  Note that `volatile'
will not help here.  Observant or source-code-reading readers may note
that there is a mention of an `ick_goto' in the source code to
C-INTERCAL; this is undocumented and this manual does not officially
claim that such a macro exists (after all, if it did, what in INTERCAL
could it possibly correspond to?), but if such a macro does exist it
obeys the same restrictions as `COME FROM'.

`FORGET' is the worst of all in terms of preserving data on the stack;
it deallocates `alloca' data and clobbers or deletes `auto' variables
in all function invocations that have come into existence since the
`NEXT' that created the topmost remaining `NEXT' stack entry was
called, or since the start of the program if the `NEXT' stack is
emptied, and the current function will continue in a new invocation.
`volatile' is useless in preventing this, because the relevant parts of
the stack where the data were stored are deleted by the command (that's
what `FORGET' does, remove stack).  If any of these data are required,
they have to be backed up into static storage (variables declared with
`static' or global variables), or into heap storage (as in with
`malloc'), or other types of storage (such as temporary files) which
are not on the stack.  (Incidentally, suddenly deleting parts of the
stack is excellent at confusing C debuggers; but even `RESUME' and
`COME FROM' tend to be sufficient to confuse such debuggers.  More
worrying is probably the fact that the C standard provides a portable
method for deleting the stack like that, and in fact the external calls
runtime library is written in standard freestanding-legal C89 (with the
exception of `+printflow' debug output which requires a hosted
implementation), meaning that in theory it would be possible to split
it out to create an implementation of a C-plus-COME-FROM-and-NEXT
language, and doing so would not be particularly difficult.)

Note that INTERCAL variables are not stored on the C stack, nor are any
of the metadata surrounding them, and so are not affected unduly by
control flow operations.


File: ick.info,  Node: Using External Calls,  Next: Expansion Libraries,  Prev: External Calls to C,  Up: External Calls

14.2 Using External Calls
=========================

Whatever language your source files are written in, when `-e' is used
(*note -e::), the compiler will go through much the same steps.

First, the INTERCAL program specified is compiled into a C program that
uses the INTERCAL external call conventions for its control flow
operations.  The resulting `.c' file will be left behind in the same
directory (even if `-g' isn't used); if you look at it, you'll see the
`#include <ick_ec.h>' line, and the other hallmarks of an external call
program (for instance, INTERCAL `NEXT's will translate into slightly
modified `ick_next's; the modification is simply to allow the correct
line number to be displayed in case of error).

After that, the resulting files are preprocessed twice.  First, the C
preprocessor is run on the files; then, a special C-INTERCAL
`preprocessor' is run on the files.  (`Preprocessor' is a bit of a
misnomer here, as it's near the end of the compilation process;
`postprocessor' would likely be more accurate, or maybe
`interprocessor'.)  Its job is to fix line labels between the gotos
that are used to implement jumping into the middle of a C function, to
assign unique numbers to things that need them, and to keep track of
which functions need to be checked for line labels and for `COME FROM's
and `NEXT FROM's.  The resulting file will have the extension `.cio';
it is almost human-readable, especially if you run it through a C code
indenter, and consists of C code (or code in whatever language is being
linked to the INTERCAL code, but so far only C is accepted) and
instructions to `gcc'.  The `.cio' file will be left behind for you to
look at, if you like.

Once the `.cio' files have been produced, `gcc' is used to compile all
the `.cio' files and link them together into an executable; the
executable will have the same name as the INTERCAL source, minus any
extension (and on DJGPP, assuming that its version of `gcc' could
handle the resulting command line (not necessarily guaranteed), a
`.exe' extension is added), and will consist of all the C files linked
together with the INTERCAL.  Any functions named `main' in the C files
will be deleted; likewise, if there is a name clash between any two
functions, the one in the file named earlier on the command line will
be used.  There is presumably some use for this feature, although I
haven't figured out what it is yet.

Extending this to other compiled languages is mostly a problem of
determining how they fit into the INTERCAL control structure, which is
not a trivial task, and of figuring out how to link them to C code,
which in some cases is trivial (especially if the language is one that
`gcc' can compile!) and in other cases is very difficult.  If anyone
has any ideas of new languages that could be added to the external
calls system, feel free to contact the current C-INTERCAL maintainer
with suggestions or patches.


File: ick.info,  Node: Expansion Libraries,  Prev: Using External Calls,  Up: External Calls

14.3 Expansion Libraries
========================

The C-INTERCAL distribution comes with libraries that can be used to
extend its capabilities; they are implemented using the external call
mechanism, and are in effect standard files to include using that
mechanism.  To use an expansion library, give the `-e' option to `ick'
(note that this means you cannot use them with the debugger or
profiler, nor with multithreaded or backtracking programs), and specify
the expansion library's name at the end of the command line (or to be
precise, anywhere after the initial INTERCAL file).  The libraries
themselves are written in C and have a `.c' extension, and are
human-readable; C-INTERCAL will look for them in the same place as it
looks for the system library (including in the current directory, so
you can test your own expansion libraries without having to install
them).

Expansion libraries use C identifiers which start with the string
`ick_my_' (this is not used by the compiler, and is explicitly not
affected by the prohibition on identifiers starting `ick_' when writing
an expansion library), and use line labels in the range (1600) to
(1699).  (Most programs will be avoiding this range anyway, because
it's inside the (1000) to (1999) range reserved for the system library,
but the system library doesn't use it, in much the same way that the
identifiers used are inside the range reserved for the compiler, but
the compiler doesn't use them.)

Expansion libraries are available from C-INTERCAL version 0.28;
CLC-INTERCAL has a similar concept (that of `preloads'), but
implemented a completely different way.

syslibc
-------

`syslibc' is an implementation of the base-2 INTERCAL system library in
C (*note System Library::); using it in programs running in other bases
is accepted by the compiler, but likely to produce unpredictable
results.  When using this expansion library, you also need to give the
`-E' option (*note -E: -E+.) so that the main system library is not
included, or it will be used in preference to the expansion library.
All documented features of the INTERCAL base-2 system library are
implemented, but most undocumented features are not, so INTERCAL
programs which relied on them (dubious behaviour in any case) will not
work with `syslibc'.  The main reason to use this library is to
increase the speed of an INTERCAL program; however, note that the speed
gains in arithmetic will be accompanied by the performance penalty of
using the external calls infrastructure, unless you were already using
it.

compunex
--------

As an example of using `ick_create', a very simple expansion library is
provided to enable a computed NEXT capability, by defining a new
command `COMPUNEX'.  It is used as `DO .1 COMPUNEX' (allowing any
expression in place of the .1), and is similar to an ordinary `NEXT',
but has two limitations: it takes up two `NEXT' stack entries, and the
top one should not be `RESUMEd' past or forgotten (thus it isn't a
particularly useful command, except maybe to produce the equivalent of
something like function pointers).  By the way, note that C-INTERCAL
avoids computed `NEXT' mainstream for much the same way that
CLC-INTERCAL avoids `NEXT' altogether; it makes things too easy.  This
example is provided mostly just to demonstrate the syntax, and the care
that needs to be taken with implementing flow control operators.


File: ick.info,  Node: Differences to Other Compilers,  Next: Character Sets,  Prev: External Calls,  Up: Top

15 Differences to Other Compilers
*********************************

The C-INTERCAL compiler exists in a world of several other compilers.

Differences to the Princeton compiler
-------------------------------------

The Princeton compiler was the first INTERCAL compiler available, and
compiled INTERCAL-72.  Using `convickt' (*note convickt::) to translate
its programs from the original EBCDIC to Latin-1 or Atari-syntax ASCII
is required to run them under the C-INTERCAL compiler, but apart from
that there should be no problems; everything that that compiler can do
can be reproduced by C-INTERCAL, even including some of its bugs.  The
only potential problems may be where constructs were nonportable or
dubious to begin with (such as the `IGNORE'/`RETRIEVE' interaction), or
where commands intended to be syntax errors were used in the program
but have a meaning in C-INTERCAL.  For extra portability, it's possible
to use the `-t' compiler option to `ick' (*note -t::) to tell it to
interpret the program as INTERCAL-72, but as C-INTERCAL's dialect of
INTERCAL is basically backward-compatible anyway this mostly serves to
check newer programs for compatibility with older compilers.

Differences to the Atari compiler
---------------------------------

The Atari compiler was another implementation of INTERCAL-72, which was
basically identical to the Princeton compiler apart from its use of
ASCII and Atari syntax.  Everything said under the previous section
applies, except that as it uses the same syntax as C-INTERCAL anyway
(C-INTERCAL's syntax was based on the Atari compiler's), there is no
need to use `convickt'.

Differences to J-INTERCAL
-------------------------

The J-INTERCAL compiler is an implementation of INTERCAL written in Java
that compiles INTERCAL into Java (and so has a similar relationship
with Java to that of the C-INTERCAL compiler (which is written in C and
compiles into C) with C).  J-INTERCAL has much the same feature set as
older versions of C-INTERCAL, with a few changes (such as the addition
of Esperanto and error messages coming up in different situations).
J-INTERCAL programs should run fine on C-INTERCAL without trouble (as
it is also an Atari syntax compiler), except in nonportable cases such
as `IGNORE'/`RETRIEVE' interaction.

Differences to CLC-INTERCAL
---------------------------

The CLC-INTERCAL compiler is the most modern INTERCAL compiler apart
from C-INTERCAL (both compilers are maintained and updated every now
and then as of the time of writing, so which is more modern is normally
a matter of when you happen to check).  Unlike the other three compilers
mentioned above, it has a quite significant feature set, including many
features not implemented or only partially implemented in C-INTERCAL,
and is responsible for the origin of many of the features added in more
recent versions of C-INTERCAL.  Generally speaking, a CLC-INTERCAL
program that uses its advanced features is unlikely to run on
C-INTERCAL, or vice versa, whatever you do (apart from completely
rewriting the more advanced parts of the program.)

However, there are certain steps that can be taken to transfer less
advanced programs from one compiler to the other.  First, translate the
program to Latin-1 Princeton syntax (if translating from CLC-INTERCAL
to C-INTERCAL) or Atari syntax (if translating from C-INTERCAL to
CLC-INTERCAL), maybe using `convickt', if necessary.  (Note that here
the program is being translated to the syntax that is not default for
the target compiler.)  Then use command-line arguments to switch the
compiler into the correct emulation mode for the other compiler;
C-INTERCAL uses the options `-xX', and on CLC-INTERCAL this is done by
selecting the appropriate preloads, or by changing the program's file
extension to `.ci'.  In each case other options may be needed to turn
on various extensions (maybe `-m' or `-v' if translating to C-INTERCAL,
maybe the preload for gerund-based `COME FROM' if translating to
CLC-INTERCAL), and if translating to CLC-INTERCAL you need to append
the system library to your program yourself because CLC-INTERCAL
doesn't load it automatically.

In the case of very simple programs, or if you want to spend the effort
in translating compiler-specific code from one compiler to another, you
may be able to work without emulation options.  (This is a good target
to aim for, in any case.)  In such a case, you would do nothing other
than possibly edit the program to be more portable and a possible
character set and syntax change using `convickt'.  If you need
compiler-specific code, you may be able to detect the compiler in the
code itself and adapt accordingly; making use of the
`IGNORE'/`RETRIEVE' interaction is one way to do this, as it differs
between C-INTERCAL, J-INTERCAL, and CLC-INTERCAL.  The other things to
watch out for when doing this are that CLC-INTERCAL needs an explicit
option to enable the use of `NEXT', that CLC-INTERCAL doesn't load the
system library itself (you need to manually append it to the end of the
program) and that you probably shouldn't number a line (666) unless you
know what you're doing, because that line number has a special meaning
in CLC-INTERCAL.


File: ick.info,  Node: Character Sets,  Next: convickt,  Prev: Differences to Other Compilers,  Up: Top

Appendix A Character Sets
*************************

The following table explains the equivalences between the various
character sets used for INTERCAL: 7-bit ASCII Atari syntax, 5-bit
Baudot Princeton syntax, 8-bit EBCDIC Princeton syntax, and 8-bit
Latin-1 Princeton syntax.  (The Baudot and EBCDIC are the CLC-INTERCAL
versions, which are used by INTERCAL compilers but basically nowhere
else.)  The characters themselves are not shown in the table below,
because they would have to be shown in some syntax, which would be
misleading.  (Atari syntax is used throughout this manual; you could
convert from that, assuming you have an ASCII table handy.)  You can
also use the `convickt' command-line tool to translate INTERCAL
programs from one format to another (*note convickt::).  Note that
Baudot has more than one 'shift state'; the shift state (1, 2, 3, or 4)
is written before the hexadecimal code for each character, and *
represents a character available in every shift state.  To change from
one shift state to another, use character 1f to change from shift
states 3 or 4 to 1, or from 1 or 2 to 2, and character 1b to change
from shift states 1 or 2 to 3, or from 3 or 4 to 4.

Atari   Baudot   EBCDIC   Latin-1
------------------------------------ 
09      N/A      09       09
0a      * 02     0a       0a
0d      * 08     0d       0d
20      * 04     40       20
21      3 0d     4f       21
22      3 11     7f       22
23      4 06     7b       23
24      4 01     4a       a2
25      4 1c     6c       25
26      3 1a     50       26
27      3 0b     7d       27
28      3 0f     4d       28
29      3 12     5d       29
2a      4 09     5c       2a
2b      4 03     4e       2b
2c      3 0c     6b       2c
2d      3 03     60       2d
2e      3 1c     4b       2e
2f      3 1d     61       2f
30      3 16     f0       30
31      3 17     f1       31
32      3 13     f2       32
33      3 01     f3       33
34      3 0a     f4       34
35      3 10     f5       35
36      3 15     f6       36
37      3 07     f7       37
38      3 06     f8       38
39      3 18     f9       39
3a      3 0e     7a       3a
3b      3 1e     5e       3b
3c      4 0f     4c       3c
3d      4 07     7e       3d
3e      4 12     6e       3e
3f      4 0c     65       a5
40      3 19     6f       3f
41      1 03     c1       41
42      1 19     c2       42
43      1 0e     c3       43
44      1 09     c4       44
45      1 01     c5       45
46      1 0d     c6       46
47      1 1a     c7       47
48      1 14     c8       48
49      1 06     c9       49
4a      1 0b     d1       4a
4b      1 0f     d2       4b
4c      1 13     d3       4c
4d      1 1c     d4       4d
4e      1 0c     d5       4e
4f      1 18     d6       4f
50      1 16     d7       50
51      1 17     d8       51
52      1 0a     d9       52
53      1 05     e2       53
54      1 10     e3       54
55      1 07     e4       55
56      1 1e     e5       56
57      1 12     e6       57
58      1 1d     e7       58
59      1 15     e8       59
5a      1 11     e9       5a
5b      4 10     9e       5b
5c      4 05     N/A      5c
5d      4 13     5a       5d
5e      4 0d     6a       7c
5f      4 15     7c       40
60      N/A      N/A      60
61      2 03     81       61
62      2 19     82       62
63      2 0e     83       63
64      2 09     84       64
65      2 01     85       65
66      2 0d     86       66
67      2 1a     87       67
68      2 14     88       68
69      2 06     89       69
6a      2 0b     91       6a
6b      2 0f     92       6b
6c      2 13     93       6c
6d      2 1c     94       6d
6e      2 0c     95       6e
6f      2 18     96       6f
70      2 16     97       70
71      2 17     98       71
72      2 0a     99       72
73      2 05     a2       73
74      2 10     a3       74
75      2 07     a4       75
76      2 1e     a5       76
77      2 12     a6       77
78      2 1d     a7       78
79      2 15     a8       79
7a      2 11     a9       7a
7b      4 0a     9c       7b
7c      4 1e     fe       N/A
7d      4 11     dc       7d
7e      4 0b     a1       7e


File: ick.info,  Node: convickt,  Next: Optimizer Idiom Language,  Prev: Character Sets,  Up: Top

Appendix B convickt
*******************

A variety of character sets have historically been used to represent
INTERCAL programs.  Atari syntax was designed specifically for use with
ASCII-7, and all Atari-syntax-based INTERCAL compilers accept that
character set as possible input.  (C-INTERCAL also accepts Latin-1 and
UTF-8.)  However, the story is more complicated with Princeton syntax;
the original Princeton compiler was designed to work with EBCDIC, but
because modern computers are often not designed to work with this
character set other character sets are often used to represent it,
particularly Latin-1.  The CLC-INTERCAL compiler accepts Latin-1, a
custom dialect of EBCDIC, Baudot, and a punched-card format as input;
C-INTERCAL can cope with Latin-1 Princeton syntax, but for the other
character sets, for other compilers, or just for getting something
human-readable, it's useful to have a conversion program.  `convickt'
is an INTERCAL character set conversion program designed with these
needs in mind.

The syntax for using `convickt' is

     convickt INPUTSET OUTPUTSET [PADDING]

(that is, the input and output character sets are compulsory, but the
parameter specifying what sort of padding to use is optional).

The following values for INPUTSET and OUTPUTSET are permissible:

`latin1'
     Latin-1, or to give it its official name ISO-8859-1, is the
     character set most commonly used for transmitting CLC-INTERCAL
     programs, and therefore nowadays the most popular character set
     for Princeton syntax programs.  Because it is identical to ASCII-7
     in all codepoints that don't have the high bit set, most of the
     characters in it can be read by most modern editors and terminals.
     It is also far more likely to be supported by modern editors than
     EBCDIC, Baudot, or punched cards, all of which have fallen into
     relative disuse since 1972.  It is also the only input character
     set that C-INTERCAL supports for Princeton syntax programs.  It
     uses 8 bit characters.

`ebcdic'
     EBCDIC is an 8-bit character set that was an alternative to ASCII
     in 1972, and is the character set used by the original Princeton
     compiler.  Unfortunately, there is no single standard version; the
     version of EBCDIC used by `convickt' is the one that CLC-INTERCAL
     uses.  It is the default input character set that CLC-INTERCAL uses
     (although more recent versions of CLC-INTERCAL instead try to
     guess the input character set based on the input program.)

`baudot'
     Baudot is a 5-bit character set with shift codes; therefore when
     storing it in a file on an 8-bit computer, padding is needed to
     fill in the remaining three bits.  The standard Baudot character
     set does not contain all the characters needed by INTERCAL;
     therefore, CLC-INTERCAL uses repeated shift codes to add two more
     sets of characters.  `convickt' uses the CLC-INTERCAL version of
     Baudot, so as to be able to translate programs designed for that
     compiler; however, standard Baudot is also accepted in input if it
     contains no redundant shift codes, and if the input contains no
     characters not in standard Baudot, the output will be written so
     that it is both correct standard Baudot and correct CLC-INTERCAL
     Baudot for those characters.

`atari'
     This option causes `convickt' to attempt a limited conversion to
     or from Atari syntax; this uses ASCII-7 as the character set, but
     also tries to translate between Atari and Princeton syntax at the
     character level, which is sometimes but not always effective.  For
     instance, `?' is translated from Atari to Princeton as a yen sign,
     and from Princeton to Atari as a whirlpool (`@'); this sort of
     behaviour is often capable of translating expressions
     automatically, but will fail when characters outside ASCII-7
     (Atari) or Latin-1 (Princeton) are used, and will not, for
     instance, translate a Princeton `V', backspace, `-' into Atari
     `?', but instead leave it untouched.  ASCII-7 is a 7-bit character
     set, so on an 8 bit computer, there is one bit of padding that
     needs to be generated; note, however, that it is usual nowadays to
     clear the top bit when transmitting ASCII-7, which the `printable'
     and `zero' padding styles will do, but the `random' style may not
     do.


When using a character set where not all bits in each byte are
specified, a third argument can be given to specify what sort of
padding to use for the top bits of each character. There are three
options for this:

Option      Meaning
----------------------------------------------------------------- 
printable   Keep the output in the range 32-126 where possible
zero        Zero the high bits in the output
random      Pad with random bits (avoiding all-zero bytes)

Note that not all conversions are possible.  If a character cannot be
converted, it will normally be converted to a NUL byte (which is
invalid in every character set); note that this will prevent
round-tripping, because NUL is interpreted as end-of-input if given in
the input.  There is one exception; if the character that could not be
converted is a tab character, it will be converted to the other
character set's representation of a space character, if possible,
because the two characters have the same meaning in INTERCAL (the only
difference is if the command is a syntax error that's printed as an
error message).  (The exception exists to make it possible to translate
existing INTERCAL source code into Baudot.)


File: ick.info,  Node: Optimizer Idiom Language,  Next: Copying,  Prev: convickt,  Up: Top

Appendix C Optimizer Idiom Language
***********************************

One file in the C-INTERCAL distribution (`src/idiotism.oil') is written
in Optimizer Idiom Language, a programming language designed especially
for expressing optimizer idioms for INTERCAL in an easily editable form
(well, at least it's easier than the unmaintainable set of idioms
hard-coded in C that were used in previous versions of the INTERCAL
compiler).

* Menu:

* Basics: OIL Basics.               The basics of how an OIL program works.
* Syntax: OIL Syntax.               How to write comments, idioms, and groups.
* Expressions: OIL Expressions.     Expressions are the basis of idioms.
* Patterns: OIL Patterns.           Filling in the left hand side of an idiom.
* Replacements: OIL Replacements.   Syntax for the right hand side.
* Loops: OIL Loops.                 Simplifying and shortening programs.
* Tips: OIL Tips.                   Some tips about using OIL.
* Example: OIL Example.             An example of how OIL can work.


File: ick.info,  Node: OIL Basics,  Next: OIL Syntax,  Up: Optimizer Idiom Language

C.1 OIL Basics
==============

The structure of an OIL file consists of a sequence of idioms.  An
optimizer idiom looks for a certain pattern in an expression (which
could be an INTERCAL expression, or an expression that has already been
partly optimized and therefore contains some non-INTERCAL operators),
and replaces it with a replacement that's `simpler' in some sense (in
the case of C-INTERCAL, `simpler' is interpreted to mean `compiles into
a faster or smaller executable when run through a C compiler').  When an
OIL program acts on an input INTERCAL file, it keeps on matching idioms
to simplify expressions, until none of the idioms act any more (and if
a situation occurs where idioms can keep matching indefinitely, the
compiler goes into an infinite loop; so don't allow that to happen); at
present, the idioms are tried from left to right, from the leaves of an
expression to its root, and from the start of the OIL file to the end;
but don't rely on that, because it's subject to change (and gets
confusing when you think about what happens when the program actually
does a replacement).  Anyway, the point is that if an idiom can match
an expression, and another idiom doesn't change it first, then the
idiom will be matched against that part of the expression eventually,
and the program won't end until there are no idioms that match the
optimized expression.

At present, the only place that OIL is used in the C-INTERCAL compiler
is when the `-O' option (*note -O: -O+.) is used in base 2.  (Syntax is
planned to extend OIL to higher bases, and some of this is documented
and even implemented, but there's no way to use it.)  The idioms are
read from the file `src/idiotism.oil' during the compilation of the
C-INTERCAL from sources; you can change the idioms, but you will then
have to recompile the distribution (and if you are using the
`config.sh' method, also reinstall, but that will be pretty fast.)


File: ick.info,  Node: OIL Syntax,  Next: OIL Expressions,  Prev: OIL Basics,  Up: Optimizer Idiom Language

C.2 OIL Syntax
==============

An OIL file is encoded as an ASCII text file using no codepoints
outside the range 0-127; using 10 for newline (as on a UNIX or Linux
system) is always acceptable, but using 13 then 10 (as is common on
Windows or DOS) for newline is acceptable only if your C compiler
recognizes that as a newline.  I have no idea what happens if you use
just 13 on an Apple computer on which that is the common newline
convention.

Comments can be given anywhere in the file by writing lines starting
with semicolons (known as hybrids to INTERCAL programmers).  It's also
possible to write a semicolon after part of a line to comment out the
rest of the line.  Inside braced C expressions, comments can be given
anywhere whitespace would be allowed by placing them between `/*' and
`*/' (in such cases, the comments will be copied verbatim to the C
temporary files used when building the C-INTERCAL compiler, where your
C compiler will ignore them).  Whitespace is ignored nearly everywhere;
the only places it isn't ignored are in the middle of a decimal
constant, inside square brackets, immediately after one of the
characters `.:#_}', and anywhere that C doesn't allow it in quoted C
code.  (This means that you can even place it inside operators like &&
if you like, as long as they're part of OIL code and not C code,
although doing this is not recommended.)  If you use whitespace in a
situation where it isn't ignored, that's almost certainly an error.

Idioms are grouped into groups of idioms by placing an identifier in
square brackets before the group; this follows the rules for C
identifiers, except that there's a maximum length of 30 characters.
This identifier is the `name' of the group, which has no effect except
on optimizer debug output; for that matter, the only effect a group has
is that all idioms in the group look the same in optimizer debug output,
because they have the same name.  It's recommended that idioms only have
the same name if they are the same idiom, possibly written in several
ways.  For example, a shift by 0 has no effect and may as well be
removed from the output; the way to express this in OIL is:

     [nullshift]
     (_1 >> #0)->(_1)
     (_1 << #0)->(_1)

Here, nullshift is the name of the group of idioms, and two idioms are
given; one which removes a null rightshift, and one which removes a null
leftshift.

As the example above shows, the syntax of an idiom itself is

     (pattern)->(replacement)

The parentheses here are actually part of the pattern and/or
replacement, and as such sparks (apostrophes) or rabbit-ears (double
quotes) can be used instead; they're shown in the syntax because the
outer layer of parenthesising is always required.  Both the pattern and
replacement are OIL expressions, although they both have their own
special syntax elements as well.


File: ick.info,  Node: OIL Expressions,  Next: OIL Patterns,  Prev: OIL Syntax,  Up: Optimizer Idiom Language

C.3 OIL Expressions
===================

An OIL expression is built around subexpressions connected by infix
binary operators and/or preceded by prefix unary operators, the same
way as in C or INTERCAL (although unary operators must be entirely
before their argument; the one character later position is not allowed.)
As in INTERCAL, there is no operator precedence; expressions must be
very fully bracketed to show unambiguously what the precedences must
be, and then more so; for instance, bracketing marks must be placed
around the argument of a unary operator in most circumstances.
Bracketing of expressions can be done with parentheses, sparks
(apostrophes) or rabbit-ears (double-quotes).

The following unary and binary operators are allowed in OIL expressions:

`$'            INTERCAL mingle
`~'            INTERCAL select
`&16'          INTERCAL unary AND (16-bit)
`V16'          INTERCAL unary OR (16-bit)
`?16'          INTERCAL unary XOR (16-bit)
`^16'          INTERCAL unary sharkfin (16-bit)
`@16'          INTERCAL unary whirlpool (16-bit)
`@216..@516'   INTERCAL unary generalised whirlpool (16-bit)
`&32'          INTERCAL unary AND (32-bit)
`V32'          INTERCAL unary OR (32-bit)
`?32'          INTERCAL unary XOR (32-bit)
`^32'          INTERCAL unary sharkfin (32-bit)
`@32'          INTERCAL unary whirlpool (32-bit)
`@232..@532'   INTERCAL unary generalised whirlpool (32-bit)
`&'            C binary bitwise AND
`|'            C binary bitwise OR
`^'            C binary bitwise XOR
`+'            C addition
`-'            C subtraction
`*'            C multiplication
`/'            C integer division
`%'            C modulus
`>'            C greater than
`<'            C less than
`~'            C unary bitwise complement
`!='           C not equals operator
`=='           C equals operator
`&&'           C logical AND
`||'           C logical OR
`>>'           C bitwise rightshift
`<<'           C bitwise leftshift
`!'            C unary logical NOT

(Note that in some cases two operators are expressed the same way, but
that this doesn't matter because one is unary and the other is binary so
that there can't be any ambiguity, only confusion.  Also note that
unlike INTERCAL unary logic operators, OIL unary logic operators must
have a bitwidth stated.)

It hasn't yet been explained what operands these operators have to
operate on; the syntax for those depends on whether it's a pattern or
replacement that the expression is representing.


File: ick.info,  Node: OIL Patterns,  Next: OIL Replacements,  Prev: OIL Expressions,  Up: Optimizer Idiom Language

C.4 OIL Patterns
================

Patterns are simply OIL expressions; the expressions match either
original INTERCAL input or expressions produced by earlier idioms.
Each operator must match the same operator in the (possibly
partially-optimised) input; the operands themselves are pattern
templates specifying what operands in the input they can match.

One special simple form of match is possible: `#NUMBER', where NUMBER
is in decimal, matches a constant with that value.  (Unlike in
INTERCAL, this constant is not limited to being a onespot value; it is,
however, limited to being at most twospot, as are all operands and
intermediate values in OIL.)

Otherwise, an operand consists of the following parts, written in order:

  1. A character to specify the data type of what's being matched.
     Usually, this will be `_' to specify that any data type can be
     matched.  In a few cases, you may want to use `.' or `:' to
     specify that you only want to match a onespot or twospot value
     respectively (that is, 16- or 32-bit).  You can also use `#'; this
     specifies a value that can be any width, but must be known to be a
     constant with a known value at optimize time (either because it
     was hardcoded as a constant originally or because a constant was
     produced there by the optimizer, for instance via a constant
     folding optimization).

  2. Optionally, an expression in braces (`{' and `}').  This
     expression is written in C, not OIL (as are all expressions in
     braces), and puts an extra condition on whether the pattern
     matches.  The exact meaning of this will be explained later.

  3. A reference number, which must be one decimal digit long.  A
     reference number of 0 causes the operand to be discarded
     immediately after matching; normally, you will want to specify a
     positive reference number.  Two operands with the same reference
     number must be exactly the same for the pattern to match (for
     instance, both references to the same variable, or identical
     subexpressions).  The reference number also allows the operand to
     be referenced by C expressions on other operands and by
     replacements.  Reference numbers must be unique within the idiom
     (unless two or reference numbers are deliberately the same so that
     the operands they reference have to be identical to produce a
     match), and they are scoped only as far as the containing idiom;
     they don't carry from one idiom to another.


Note that syntax like `#2' is ambiguous given what comes so far; the
first interpretation is the one that is taken in practice, and if the
second interpretation is wanted the operand should be expressed as
`#{1}2', using a no-op braced expression to tell them apart.  This
particular no-op is recommended because it's detected and optimized by
the `OIL' compiler.

Braced expressions, which must be written purely in C, add extra
conditions; they must return nonzero to allow a possible match or zero
to prevent one.  They can reference the following variables and
functions:

`c'
`cNUMBER'
     This accesses a calculation made automatically by the compiled OIL
     program to identify which bits of the operand can possibly be set,
     and which ones cannot be.  `c' by itself refers to the operand to
     which the braced expression is attached; if a number is given, it
     refers to another node (the number is interpreted as a reference
     numer).  The actual value of `c' is a 32-bit unsigned integer,
     each bit of which is true, or 1, if there is any chance that the
     corresponding bit of the operand might be 1, and false, or 0, if
     it's known for certain that the corresponding bit of the operand
     is 0.

     For instance:

          _{!(c&4294901760LU)}1

     The constant given here is FFFF0000 when expressed in hexadecimal;
     the point is that the expression matches any operand that is known
     to have a value no greater than 65535.  Unless the operand is the
     argument to a unary AND, this check generally makes more point
     than explicitly specifying `.' rather than `_', because it will
     identify both 16- and 32-bit values as long as they're small
     enough to fit into a onespot variable.  This code could, for
     instance, be used to check that an argument to a mingle must be
     small enough before optimising it (this is important because an
     optimisation shouldn't optimise an error - in this case, an
     overflowing mingle - into a non-error).

`x'
`xNUMBER'
     `x' is like `c', and refers to operands in the same way, except
     that it can only refer to an operand marked with `#'.  It holds
     the value of that constant (a 32-bit unsigned integer), which will
     be known to the optimizer at optimize time.  One common use of
     this is to detect whether a constant happens to be a power of 2,
     although there are many other possibilities that may be useful.

`r'
     When inside a loop, `r' is the value of the loop counter.  (It's
     almost certainly a mistake if you have a loop but don't reference
     the loop counter at least once, and usually at least twice, within
     the loop.)  *Note OIL Loops::.

`and16'
`and32'
`or16'
`or32'
`xor16'
`xor32'
`iselect'
`mingle'
     These are all functions with one argument (apart from iselect and
     mingle, which each take two arguments); they exist so that INTERCAL
     operators can be used by C expressions.  They all take unsigned
     longs as input and output, even if they are onespot operators.
     Note that it's entirely possible for these to cause a compile-time
     error if used on invalid arguments (such as mingling with an
     operand over 65535), or to silently truncate an invalid argument
     down to the right number of bits; both of these should be avoided
     if possible, so the optimiser should check first to make sure that
     it doesn't use any of these functions on invalid arguments.

`xselx'
     This function returns its argument selected with itself; so
     `xselx(c)' is shorthand for `iselect(c,c)'.  When the argument is
     very complicated, this can save a lot of space in the original OIL
     program.

`setbitcount'
     This function simply returns the number of bits with value 1 in its
     argument.  This is sometimes useful with respect to various
     select-related optimisations, and can be a useful alternative to
     having to take logarithms in various situations.

`smudgeright'
`smudgeleft'
     The `smudgeright' function returns its argument but with all the
     bits less significant than the most significant bit with value 1
     set to 1; likewise, `smudgeleft' returns its argument with all the
     bits more significant than the least significant bit with value 1
     set to 1.


Note that all OIL character is done internally using unsigned 32-bit
numbers, and C expressions you write should do the same.  The practical
upshot of this is that you should write `LU' after any constant you
write in C code; if you don't do this, you are reasonably likely to get
compiler warnings, and the resulting program may not work reliably,
although the OIL compiler itself will not complain.

Here's a more complicated example of an optimizer operand:

     #{!(x&2863311530LU)&&iselect(x,1431655765LU)==
       xselx(iselect(x,1431655765LU))}3

It helps to understand this if you know that 2863311530 in hexadecimal
is AAAAAAAA and 1431655765 is hexadecimal is 55555555.  (It's worth
putting a comment with some frequently-used decimal constants in an OIL
input file to help explain what these numbers mean and make the code
more maintainable.)  The operand matches any constant integer which has
no bits in common with AAAAAAAA, and for which if any bit in common
with 55555555 is set, all less significant bits in common with that
number are also set.


File: ick.info,  Node: OIL Replacements,  Next: OIL Loops,  Prev: OIL Patterns,  Up: Optimizer Idiom Language

C.5 OIL Replacements
====================

Replacements have much the same syntax as patterns.  The expressions are
parsed in much the same way; however, one peculiarity of replacements is
that bitwidths must be specified.  INTERCAL has a typecaster that
figures out whether each expression is 16 bits or 32 bits wide, but it
runs before the optimizer, and as the optimizer can produce expressions
whose bitwidths don't obey INTERCAL's rules, this information needs to
be inserted somehow in a replacement.  In C-INTERCAL, it usually
doesn't matter what the bitwidth is, and in cases where it doesn't
matter the normal operators (`$', `~', and so on) can be used.  (Note
that the bit width of the entire replacement is always set to the same
bit width as the bit width of the expression matched by the pattern; so
you don't have to worry about the effect on unary logical operators
that might be operating on the expression being optimized.  This is an
exception to the normal bitwidth rules for a replacement.)  In cases
where it does matter (due to C-INTERCAL's lenient interpretation of
bitwidth on mingle inputs, the only place it matters is in the input to
INTERCAL unary logical operators), both the bitwidth of the operator
and the argument on which it operates must be explicitly given, and
given as the same value; to set the bitwidth of an operator's result,
simply write the bitwidth (16 or 32 for onespot and twospot
respectively) immediately after the operator; for instance, `!=32' will
generate a not-equals operation with a 32-bit bitwidth.  If an
operator's width is set to 16, and during the course of execution of
the optimized program, a value that doesn't fit into 16 bits is
encountered, that's undefined behaviour and anything might happen (most
likely, though, the program will just act as though its width had been
set to 32 bits instead); this error condition is not detected.  Also
note that operators like `&32' already have a bitwidth specified, so
specifying `&3232' (or worse, `&3216') is not allowed.

Replacement operands are simpler than pattern operands, because there
are only a few forms they can take.

`_NUMBER'
`.NUMBER'
`:NUMBER'
     This tells the optimiser to copy the operand or expression with
     reference number NUMBER to this point in the replacement used for
     the expression matched by the pattern.  The three forms are
     identical; the last two are provided for aesthetic reasons (it can
     look better and be clearer to match `.1' in the pattern with `.1'
     in the replacement, for instance).  You cannot use `#NUMBER' here
     to copy in a constant from the left-hand side, though, nor
     `#{1}NUMBER', because the first means something else and the
     second is undefined behaviour (that is, no behaviour for the second
     case has been specifically implemented in the compiler and
     therefore its behaviour is unpredictable and subject to change in
     future versions); use `_NUMBER' to copy over a constant with an
     unknown at optimizer compile time (but known at optimize time)
     value from the left hand side, as you can do with any other
     operand being copied.

`#NUMBER'
     Insert a constant with the literal value NUMBER here.

`#{EXPRESSION}0'
     Calculate the value of EXPRESSION (a C expression, which can
     reference the same variables and functions as a C expression in a
     pattern can); see *Note C functions in OIL::.


As an example, here's an idiom that moves C bitwise AND operations
inside leftshifts.  (This is useful because if the optimizer has
generated a large sequence of mixed ANDs and bitshifts, moving all the
ANDs to one end allows them to be clumped together and optimized down to
one AND.)

     ((_1 << #{1}2) & #{1}3)->((_1 & #{x3>>x2}0) << _2)


File: ick.info,  Node: OIL Loops,  Next: OIL Tips,  Prev: OIL Replacements,  Up: Optimizer Idiom Language

C.6 OIL Loops
=============

When writing idioms, sometimes instead of using very complicated
expressions to try to match multiple situations at once it's easier to
have a separate idiom for each possible situation; for instance, it's
easier to write idioms for right-shift by 1, right-shift by 2,
right-shift by 3, etc., rather than a general idiom to rightshift by any
amount.  When the idioms follow a pattern, as they will do in basically
every case of this sort, it's possible to automatically generate them
using a loop.  For instance, idioms to optimize a one-bit rightshift
and a two-bit rightshift are:

     (_1~#{xselx(x)<<1==x&&x}2)->((_1&_2)>>#1)
     (_1~#{xselx(x)<<2==x&&x}2)->((_1&_2)>>#2)

Adding a loop to automatically generate the idioms, and placing a name
for the group of idioms at the start, produces the following code:

     [rshift]
     <#1-#31
     (_1~#{xselx(x)<<r==x&&x}2)->((_1&_2)>>#{r}0)
     >

That's 31 different idioms, generated with a loop.  As the above example
shows, a loop starts with `<#NUMBER-#NUMBER' and ends with `>'; a
different idiom is generated for each possible value of the loop
counter `r' in the range given by the opening line of the loop.  Loops
must be placed around idioms, but inside a group of idioms.  Note the
use of `#{r}0' to generate a constant whose value is equal to the value
of the loop counter.


File: ick.info,  Node: OIL Tips,  Next: OIL Example,  Prev: OIL Loops,  Up: Optimizer Idiom Language

C.7 OIL Tips
============

Here are some tips for the best use of OIL:

   * The OIL compiler has a few deficiencies, such as error messages
     that don't give you much of an idea of what you did wrong (to
     compensate for this, it does give a reasonably accurate line and
     character number where the error happened), limits on things like
     how deep expressions can be nested and how many idioms are allowed
     (if you hit the first, you should really break it up into smaller
     idioms if possible, and if you hit the second, increase
     `MAXTOFREE' in oil.y; this isn't a limit on the number of idioms
     but on the number of strings that are allocated internally to
     process the idioms), and lack of error checking (invalid OIL may
     produce errors in the OIL compiler, or cause the output C code to
     contain errors or warnings, or may even appear to work).

   * When you have symmetrical operators in an idiom (like C binary
     logical operators), you need to write the idiom both ways round
     (in the same group of idioms, preferably), or write another idiom
     to standardise the format first; the first method can get very
     tedious when there are many symmetrical operators in an idiom, and
     the second is prone to optimizer loops and subtle errors (both
     methods have been used in the provided `idiotism.oil' file.)

   * Idioms should preferably be as general as possible, broken down
     into many separate idioms rather than all as one big idiom, and
     match the smallest part of the expression being optimized that is
     necessary for the idiom to be correct in all circumstances; all of
     these help to improve the performance of the optimizer in terms of
     what it can optimize.

   * If a program's optimizing incorrectly, or you just want to see how
     the optimizer deals with a particular program, it's possible to
     debug the optimizer by giving the `-h', `-H', or `-hH' (*note
     -h::) switch to the C-INTERCAL compiler, which will cause debug
     information to be output on stderr.  `-h' will show the initial
     and final expressions for each expression that was given as input
     to the optimizer, as well as a list of all optimizations used, in
     a language that's a sort of mix of C, INTERCAL, and OIL; `-H' will
     do the same, and also show the intermediate stages in the
     optimization.  `-hH' is like `-H', but produces its output
     entirely in C, so that the various intermediate stages can be
     tried with a C compiler, or for people who are fed up of reading
     INTERCAL.  `-H' can be a useful learning resource for people who
     want to understand how a particular INTERCAL expression works.

   * Make sure that the optimizer doesn't change a statement from a
     run-time error into something that silently succeeds!  Checking
     which bits can and can't be 1 is one good way to avoid this,
     especially with mingles.  (At present, there are some idioms that
     can turn run-time errors into compile-time errors, such as with
     the expression `''#65535$#65535'$#0''; this could be avoided, but
     for the time being it isn't.)

   * You can help!  If you find an idiom that the optimizer isn't
     optimizing correctly, feel free to add it, or multiple idioms that
     come to the same thing, to `idiotism.oil'.  In such a case, it
     would help other users if you would submit your new optimizer
     idiom to the project (*note Reporting Bugs::); this will help
     other users and future releases of INTERCAL, and also has a chance
     of allowing other users to check your new idioms to see if they
     cause problems or could be written better.



File: ick.info,  Node: OIL Example,  Prev: OIL Tips,  Up: Optimizer Idiom Language

C.8 OIL Example
===============

To finish off this appendix, here's an example of the power of OIL;
this is the optimization of an idiom from the INTERCAL-72 system
library, as shown with `-H'; this should give a good idea of how OIL
programs work.  (All the relevant idioms are in `idiotism.oil' as of
the time of writing.)  Note how the expression is reduced one small
step at a time; the smallness of the steps makes the optimizer more
general, because if the original expression had been slightly
different, the optimizer wouldn't have come to the same result but
could have optimized it quite a bit of the way, up to the point where
the optimizations were no longer valid; in an older version of
INTERCAL, this idiom was simply hardcoded as a special case and so
slight variations of it weren't optimized at all.  If you look at the
idioms themselves, it'll also be apparent how `c' (the record of which
bits of an expression can be 1 and which bits can't be) is important
information in being able to apply an optimization more aggressively.

     .3 <- ((((((((.3 $ 0x0) ~ (0x7fff $ 0x1)) $ 0x0) ~ (0x7fff $ 0x1))
     $ 0x0) ~ (0x3fff $ 0x3)) $ 0x0) ~ (0xfff $ 0xf))
     [minglefold]
     .3 <- ((((((((.3 $ 0x0) ~ 0x2aaaaaab) $ 0x0) ~ (0x7fff $ 0x1)) $
     0x0) ~ (0x3fff $ 0x3)) $ 0x0) ~ (0xfff $ 0xf))
     [lshift16]
     .3 <- ((((((((((.3 >> 0x0) & 0x7fff) << 0x1) | 0x0) $ 0x0) ~
     (0x7fff $ 0x1)) $ 0x0) ~ (0x3fff $ 0x3)) $ 0x0) ~ (0xfff $ 0xf))
     [noopor]
     .3 <- (((((((((.3 >> 0x0) & 0x7fff) << 0x1) $ 0x0) ~ (0x7fff $
     0x1)) $ 0x0) ~ (0x3fff $ 0x3)) $ 0x0) ~ (0xfff $ 0xf))
     [minglefold]
     .3 <- (((((((((.3 >> 0x0) & 0x7fff) << 0x1) $ 0x0) ~ 0x2aaaaaab) $
     0x0) ~ (0x3fff $ 0x3)) $ 0x0) ~ (0xfff $ 0xf))
     [lshift16]
     .3 <- (((((((((((.3 >> 0x0) & 0x7fff) << 0x1) >> 0x0) & 0x7fff) <<
     0x1) | 0x0) $ 0x0) ~ (0x3fff $ 0x3)) $ 0x0) ~ (0xfff $ 0xf))
     [noopor]
     .3 <- ((((((((((.3 >> 0x0) & 0x7fff) << 0x1) >> 0x0) & 0x7fff) <<
     0x1) $ 0x0) ~ (0x3fff $ 0x3)) $ 0x0) ~ (0xfff $ 0xf))
     [minglefold]
     .3 <- ((((((((((.3 >> 0x0) & 0x7fff) << 0x1) >> 0x0) & 0x7fff) <<
     0x1) $ 0x0) ~ 0xaaaaaaf) $ 0x0) ~ (0xfff $ 0xf))
     [lshift16]
     .3 <- ((((((((((((.3 >> 0x0) & 0x7fff) << 0x1) >> 0x0) & 0x7fff)
     << 0x1) >> 0x1) & 0x1fff) << 0x3) | 0x0) $ 0x0) ~ (0xfff $ 0xf))
     [noopor]
     .3 <- (((((((((((.3 >> 0x0) & 0x7fff) << 0x1) >> 0x0) & 0x7fff) <<
     0x1) >> 0x1) & 0x1fff) << 0x3) $ 0x0) ~ (0xfff $ 0xf))
     [minglefold]
     .3 <- (((((((((((.3 >> 0x0) & 0x7fff) << 0x1) >> 0x0) & 0x7fff) <<
     0x1) >> 0x1) & 0x1fff) << 0x3) $ 0x0) ~ 0xaaaaff)
     [lshift16]
     .3 <- (((((((((((((.3 >> 0x0) & 0x7fff) << 0x1) >> 0x0) & 0x7fff)
     << 0x1) >> 0x1) & 0x1fff) << 0x3) >> 0x3) & 0x1ff) << 0x7) | 0x0)
     [noopor]
     .3 <- ((((((((((((.3 >> 0x0) & 0x7fff) << 0x1) >> 0x0) & 0x7fff)
     << 0x1) >> 0x1) & 0x1fff) << 0x3) >> 0x3) & 0x1ff) << 0x7)
     [nullshift]
     .3 <- (((((((((((.3 & 0x7fff) << 0x1) >> 0x0) & 0x7fff) << 0x1) >>
     0x1) & 0x1fff) << 0x3) >> 0x3) & 0x1ff) << 0x7)
     [combinelrshift]
     .3 <- ((((((((((.3 & 0x7fff) << 0x1) & 0x7fff) << 0x1) >> 0x1) &
     0x1fff) << 0x3) >> 0x3) & 0x1ff) << 0x7)
     [andintolshift]
     .3 <- ((((((((((.3 & 0x7fff) & 0x3fff) << 0x1) << 0x1) >> 0x1) &
     0x1fff) << 0x3) >> 0x3) & 0x1ff) << 0x7)
     [combinellshift]
     .3 <- (((((((((.3 & 0x7fff) & 0x3fff) << 0x2) >> 0x1) & 0x1fff) <<
     0x3) >> 0x3) & 0x1ff) << 0x7)
     [combinelrshift]
     .3 <- ((((((((.3 & 0x7fff) & 0x3fff) << 0x1) & 0x1fff) << 0x3) >>
     0x3) & 0x1ff) << 0x7)
     [andintolshift]
     .3 <- ((((((((.3 & 0x7fff) & 0x3fff) & 0xfff) << 0x1) << 0x3) >>
     0x3) & 0x1ff) << 0x7)
     [combinellshift]
     .3 <- (((((((.3 & 0x7fff) & 0x3fff) & 0xfff) << 0x4) >> 0x3) &
     0x1ff) << 0x7)
     [combinelrshift]
     .3 <- ((((((.3 & 0x7fff) & 0x3fff) & 0xfff) << 0x1) & 0x1ff) <<
     0x7)
     [andintolshift]
     .3 <- ((((((.3 & 0x7fff) & 0x3fff) & 0xfff) & 0xff) << 0x1) << 0x7)
     [combinellshift]
     .3 <- (((((.3 & 0x7fff) & 0x3fff) & 0xfff) & 0xff) << 0x8)
     [combineand]
     .3 <- ((((.3 & 0x3fff) & 0xfff) & 0xff) << 0x8)
     [combineand]
     .3 <- (((.3 & 0xfff) & 0xff) << 0x8)
     [combineand]
     .3 <- ((.3 & 0xff) << 0x8)


File: ick.info,  Node: Copying,  Next: Main Index,  Prev: Optimizer Idiom Language,  Up: Top

Appendix D Copying
******************

The majority of the files in the C-INTERCAL distribution are licensed
under the GNU General Public License (version 2 or later), but with
some exceptions.  The files `ick-wrap.c' and `pickwrap.c' are licensed
under a license that allows them to be used for any purpose and
redistributed at will, and are explicitly not GPL'd.  This means that C
source code generated by the compiler has the same copyright conditions
as the original INTERCAL source.  (Note that the libraries `libick.a'
and `libickmt.a' are GPL, though, so you cannot redistribute an
executable produced by `ick' or by linking a C file to either of those
libraries unless the original INTERCAL source was GPL.)  For similar
reasons, the expansion library `syslibc.c' (currently the only one in
the distribution) is explicitly public domain.  Also, this manual, and
the files that are the source code for creating it, are licensed under
the GNU Free Documentation License rather than the GPL, and the
licenses themselves (`fdl-1-2.txi' and `COPYING.txt') are licensed
under a license that allows verbatim redistribution but not creation of
derivative works.  All other files, though (including the `man' pages,
which are not part of _this_ manual), are licensed under the GPL.  For
the full text of the GPL, see the file `COPYING.txt' in the
distribution.

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