SCM ¶

1.3.1 The SCM License ¶

This program is free software: you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public License along with this program. If not, see http://www.gnu.org/licenses/.

1.3.2 SIOD copyright ¶

Permission to use, copy, modify, distribute and sell this software and its documentation for any purpose and without fee is hereby granted, provided that the above copyright notice appear in all copies and that both that copyright notice and this permission notice appear in supporting documentation, and that the name of Paradigm Associates Inc not be used in advertising or publicity pertaining to distribution of the software without specific, written prior permission.

PARADIGM DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO EVENT SHALL PARADIGM BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

gjc@paradigm.com

1.3.3 GNU Free Documentation License ¶

Copyright © 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc.
http://fsf.org/

Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.

0. PREAMBLE

   The purpose of this License is to make a manual, textbook, or other functional and useful document free in the sense of freedom: to assure everyone the effective freedom to copy and redistribute it, with or without modifying it, either commercially or noncommercially. Secondarily, this License preserves for the author and publisher a way to get credit for their work, while not being considered responsible for modifications made by others.

   This License is a kind of “copyleft”, which means that derivative works of the document must themselves be free in the same sense. It complements the GNU General Public License, which is a copyleft license designed for free software.

   We have designed this License in order to use it for manuals for free software, because free software needs free documentation: a free program should come with manuals providing the same freedoms that the software does. But this License is not limited to software manuals; it can be used for any textual work, regardless of subject matter or whether it is published as a printed book. We recommend this License principally for works whose purpose is instruction or reference.

1. APPLICABILITY AND DEFINITIONS

   This License applies to any manual or other work, in any medium, that contains a notice placed by the copyright holder saying it can be distributed under the terms of this License. Such a notice grants a world-wide, royalty-free license, unlimited in duration, to use that work under the conditions stated herein. The “Document”, below, refers to any such manual or work. Any member of the public is a licensee, and is addressed as “you”. You accept the license if you copy, modify or distribute the work in a way requiring permission under copyright law.

   A “Modified Version” of the Document means any work containing the Document or a portion of it, either copied verbatim, or with modifications and/or translated into another language.

   A “Secondary Section” is a named appendix or a front-matter section of the Document that deals exclusively with the relationship of the publishers or authors of the Document to the Document’s overall subject (or to related matters) and contains nothing that could fall directly within that overall subject. (Thus, if the Document is in part a textbook of mathematics, a Secondary Section may not explain any mathematics.) The relationship could be a matter of historical connection with the subject or with related matters, or of legal, commercial, philosophical, ethical or political position regarding them.

   The “Invariant Sections” are certain Secondary Sections whose titles are designated, as being those of Invariant Sections, in the notice that says that the Document is released under this License. If a section does not fit the above definition of Secondary then it is not allowed to be designated as Invariant. The Document may contain zero Invariant Sections. If the Document does not identify any Invariant Sections then there are none.

   The “Cover Texts” are certain short passages of text that are listed, as Front-Cover Texts or Back-Cover Texts, in the notice that says that the Document is released under this License. A Front-Cover Text may be at most 5 words, and a Back-Cover Text may be at most 25 words.

   A “Transparent” copy of the Document means a machine-readable copy, represented in a format whose specification is available to the general public, that is suitable for revising the document straightforwardly with generic text editors or (for images composed of pixels) generic paint programs or (for drawings) some widely available drawing editor, and that is suitable for input to text formatters or for automatic translation to a variety of formats suitable for input to text formatters. A copy made in an otherwise Transparent file format whose markup, or absence of markup, has been arranged to thwart or discourage subsequent modification by readers is not Transparent. An image format is not Transparent if used for any substantial amount of text. A copy that is not “Transparent” is called “Opaque”.

   Examples of suitable formats for Transparent copies include plain ASCII without markup, Texinfo input format, LaTeX input format, SGML or XML using a publicly available DTD, and standard-conforming simple HTML, PostScript or PDF designed for human modification. Examples of transparent image formats include PNG, XCF and JPG. Opaque formats include proprietary formats that can be read and edited only by proprietary word processors, SGML or XML for which the DTD and/or processing tools are not generally available, and the machine-generated HTML, PostScript or PDF produced by some word processors for output purposes only.

   The “Title Page” means, for a printed book, the title page itself, plus such following pages as are needed to hold, legibly, the material this License requires to appear in the title page. For works in formats which do not have any title page as such, “Title Page” means the text near the most prominent appearance of the work’s title, preceding the beginning of the body of the text.

   The “publisher” means any person or entity that distributes copies of the Document to the public.

   A section “Entitled XYZ” means a named subunit of the Document whose title either is precisely XYZ or contains XYZ in parentheses following text that translates XYZ in another language. (Here XYZ stands for a specific section name mentioned below, such as “Acknowledgements”, “Dedications”, “Endorsements”, or “History”.) To “Preserve the Title” of such a section when you modify the Document means that it remains a section “Entitled XYZ” according to this definition.

   The Document may include Warranty Disclaimers next to the notice which states that this License applies to the Document. These Warranty Disclaimers are considered to be included by reference in this License, but only as regards disclaiming warranties: any other implication that these Warranty Disclaimers may have is void and has no effect on the meaning of this License.

2. VERBATIM COPYING

   You may copy and distribute the Document in any medium, either commercially or noncommercially, provided that this License, the copyright notices, and the license notice saying this License applies to the Document are reproduced in all copies, and that you add no other conditions whatsoever to those of this License. You may not use technical measures to obstruct or control the reading or further copying of the copies you make or distribute. However, you may accept compensation in exchange for copies. If you distribute a large enough number of copies you must also follow the conditions in section 3.

   You may also lend copies, under the same conditions stated above, and you may publicly display copies.

3. COPYING IN QUANTITY

   If you publish printed copies (or copies in media that commonly have printed covers) of the Document, numbering more than 100, and the Document’s license notice requires Cover Texts, you must enclose the copies in covers that carry, clearly and legibly, all these Cover Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on the back cover. Both covers must also clearly and legibly identify you as the publisher of these copies. The front cover must present the full title with all words of the title equally prominent and visible. You may add other material on the covers in addition. Copying with changes limited to the covers, as long as they preserve the title of the Document and satisfy these conditions, can be treated as verbatim copying in other respects.

   If the required texts for either cover are too voluminous to fit legibly, you should put the first ones listed (as many as fit reasonably) on the actual cover, and continue the rest onto adjacent pages.

   If you publish or distribute Opaque copies of the Document numbering more than 100, you must either include a machine-readable Transparent copy along with each Opaque copy, or state in or with each Opaque copy a computer-network location from which the general network-using public has access to download using public-standard network protocols a complete Transparent copy of the Document, free of added material. If you use the latter option, you must take reasonably prudent steps, when you begin distribution of Opaque copies in quantity, to ensure that this Transparent copy will remain thus accessible at the stated location until at least one year after the last time you distribute an Opaque copy (directly or through your agents or retailers) of that edition to the public.

   It is requested, but not required, that you contact the authors of the Document well before redistributing any large number of copies, to give them a chance to provide you with an updated version of the Document.

4. MODIFICATIONS

   You may copy and distribute a Modified Version of the Document under the conditions of sections 2 and 3 above, provided that you release the Modified Version under precisely this License, with the Modified Version filling the role of the Document, thus licensing distribution and modification of the Modified Version to whoever possesses a copy of it. In addition, you must do these things in the Modified Version:

   1. Use in the Title Page (and on the covers, if any) a title distinct from that of the Document, and from those of previous versions (which should, if there were any, be listed in the History section of the Document). You may use the same title as a previous version if the original publisher of that version gives permission.
   2. List on the Title Page, as authors, one or more persons or entities responsible for authorship of the modifications in the Modified Version, together with at least five of the principal authors of the Document (all of its principal authors, if it has fewer than five), unless they release you from this requirement.
   3. State on the Title page the name of the publisher of the Modified Version, as the publisher.
   4. Preserve all the copyright notices of the Document.
   5. Add an appropriate copyright notice for your modifications adjacent to the other copyright notices.
   6. Include, immediately after the copyright notices, a license notice giving the public permission to use the Modified Version under the terms of this License, in the form shown in the Addendum below.
   7. Preserve in that license notice the full lists of Invariant Sections and required Cover Texts given in the Document’s license notice.
   8. Include an unaltered copy of this License.
   9. Preserve the section Entitled “History”, Preserve its Title, and add to it an item stating at least the title, year, new authors, and publisher of the Modified Version as given on the Title Page. If there is no section Entitled “History” in the Document, create one stating the title, year, authors, and publisher of the Document as given on its Title Page, then add an item describing the Modified Version as stated in the previous sentence.
   10. Preserve the network location, if any, given in the Document for public access to a Transparent copy of the Document, and likewise the network locations given in the Document for previous versions it was based on. These may be placed in the “History” section. You may omit a network location for a work that was published at least four years before the Document itself, or if the original publisher of the version it refers to gives permission.
   11. For any section Entitled “Acknowledgements” or “Dedications”, Preserve the Title of the section, and preserve in the section all the substance and tone of each of the contributor acknowledgements and/or dedications given therein.
   12. Preserve all the Invariant Sections of the Document, unaltered in their text and in their titles. Section numbers or the equivalent are not considered part of the section titles.
   13. Delete any section Entitled “Endorsements”. Such a section may not be included in the Modified Version.
   14. Do not retitle any existing section to be Entitled “Endorsements” or to conflict in title with any Invariant Section.
   15. Preserve any Warranty Disclaimers.

   If the Modified Version includes new front-matter sections or appendices that qualify as Secondary Sections and contain no material copied from the Document, you may at your option designate some or all of these sections as invariant. To do this, add their titles to the list of Invariant Sections in the Modified Version’s license notice. These titles must be distinct from any other section titles.

   You may add a section Entitled “Endorsements”, provided it contains nothing but endorsements of your Modified Version by various parties—for example, statements of peer review or that the text has been approved by an organization as the authoritative definition of a standard.

   You may add a passage of up to five words as a Front-Cover Text, and a passage of up to 25 words as a Back-Cover Text, to the end of the list of Cover Texts in the Modified Version. Only one passage of Front-Cover Text and one of Back-Cover Text may be added by (or through arrangements made by) any one entity. If the Document already includes a cover text for the same cover, previously added by you or by arrangement made by the same entity you are acting on behalf of, you may not add another; but you may replace the old one, on explicit permission from the previous publisher that added the old one.

   The author(s) and publisher(s) of the Document do not by this License give permission to use their names for publicity for or to assert or imply endorsement of any Modified Version.

5. COMBINING DOCUMENTS

   You may combine the Document with other documents released under this License, under the terms defined in section 4 above for modified versions, provided that you include in the combination all of the Invariant Sections of all of the original documents, unmodified, and list them all as Invariant Sections of your combined work in its license notice, and that you preserve all their Warranty Disclaimers.

   The combined work need only contain one copy of this License, and multiple identical Invariant Sections may be replaced with a single copy. If there are multiple Invariant Sections with the same name but different contents, make the title of each such section unique by adding at the end of it, in parentheses, the name of the original author or publisher of that section if known, or else a unique number. Make the same adjustment to the section titles in the list of Invariant Sections in the license notice of the combined work.

   In the combination, you must combine any sections Entitled “History” in the various original documents, forming one section Entitled “History”; likewise combine any sections Entitled “Acknowledgements”, and any sections Entitled “Dedications”. You must delete all sections Entitled “Endorsements.”

6. COLLECTIONS OF DOCUMENTS

   You may make a collection consisting of the Document and other documents released under this License, and replace the individual copies of this License in the various documents with a single copy that is included in the collection, provided that you follow the rules of this License for verbatim copying of each of the documents in all other respects.

   You may extract a single document from such a collection, and distribute it individually under this License, provided you insert a copy of this License into the extracted document, and follow this License in all other respects regarding verbatim copying of that document.

7. AGGREGATION WITH INDEPENDENT WORKS

   A compilation of the Document or its derivatives with other separate and independent documents or works, in or on a volume of a storage or distribution medium, is called an “aggregate” if the copyright resulting from the compilation is not used to limit the legal rights of the compilation’s users beyond what the individual works permit. When the Document is included in an aggregate, this License does not apply to the other works in the aggregate which are not themselves derivative works of the Document.

   If the Cover Text requirement of section 3 is applicable to these copies of the Document, then if the Document is less than one half of the entire aggregate, the Document’s Cover Texts may be placed on covers that bracket the Document within the aggregate, or the electronic equivalent of covers if the Document is in electronic form. Otherwise they must appear on printed covers that bracket the whole aggregate.

8. TRANSLATION

   Translation is considered a kind of modification, so you may distribute translations of the Document under the terms of section 4. Replacing Invariant Sections with translations requires special permission from their copyright holders, but you may include translations of some or all Invariant Sections in addition to the original versions of these Invariant Sections. You may include a translation of this License, and all the license notices in the Document, and any Warranty Disclaimers, provided that you also include the original English version of this License and the original versions of those notices and disclaimers. In case of a disagreement between the translation and the original version of this License or a notice or disclaimer, the original version will prevail.

   If a section in the Document is Entitled “Acknowledgements”, “Dedications”, or “History”, the requirement (section 4) to Preserve its Title (section 1) will typically require changing the actual title.

9. TERMINATION

   You may not copy, modify, sublicense, or distribute the Document except as expressly provided under this License. Any attempt otherwise to copy, modify, sublicense, or distribute it is void, and will automatically terminate your rights under this License.

   However, if you cease all violation of this License, then your license from a particular copyright holder is reinstated (a) provisionally, unless and until the copyright holder explicitly and finally terminates your license, and (b) permanently, if the copyright holder fails to notify you of the violation by some reasonable means prior to 60 days after the cessation.

   Moreover, your license from a particular copyright holder is reinstated permanently if the copyright holder notifies you of the violation by some reasonable means, this is the first time you have received notice of violation of this License (for any work) from that copyright holder, and you cure the violation prior to 30 days after your receipt of the notice.

   Termination of your rights under this section does not terminate the licenses of parties who have received copies or rights from you under this License. If your rights have been terminated and not permanently reinstated, receipt of a copy of some or all of the same material does not give you any rights to use it.

10. FUTURE REVISIONS OF THIS LICENSE

    The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. See http://www.gnu.org/copyleft/.

    Each version of the License is given a distinguishing version number. If the Document specifies that a particular numbered version of this License “or any later version” applies to it, you have the option of following the terms and conditions either of that specified version or of any later version that has been published (not as a draft) by the Free Software Foundation. If the Document does not specify a version number of this License, you may choose any version ever published (not as a draft) by the Free Software Foundation. If the Document specifies that a proxy can decide which future versions of this License can be used, that proxy’s public statement of acceptance of a version permanently authorizes you to choose that version for the Document.

11. RELICENSING

    “Massive Multiauthor Collaboration Site” (or “MMC Site”) means any World Wide Web server that publishes copyrightable works and also provides prominent facilities for anybody to edit those works. A public wiki that anybody can edit is an example of such a server. A “Massive Multiauthor Collaboration” (or “MMC”) contained in the site means any set of copyrightable works thus published on the MMC site.

    “CC-BY-SA” means the Creative Commons Attribution-Share Alike 3.0 license published by Creative Commons Corporation, a not-for-profit corporation with a principal place of business in San Francisco, California, as well as future copyleft versions of that license published by that same organization.

    “Incorporate” means to publish or republish a Document, in whole or in part, as part of another Document.

    An MMC is “eligible for relicensing” if it is licensed under this License, and if all works that were first published under this License somewhere other than this MMC, and subsequently incorporated in whole or in part into the MMC, (1) had no cover texts or invariant sections, and (2) were thus incorporated prior to November 1, 2008.

    The operator of an MMC Site may republish an MMC contained in the site under CC-BY-SA on the same site at any time before August 1, 2009, provided the MMC is eligible for relicensing.

ADDENDUM: How to use this License for your documents ¶

To use this License in a document you have written, include a copy of the License in the document and put the following copyright and license notices just after the title page:

  Copyright (C)  year  your name.
  Permission is granted to copy, distribute and/or modify this document
  under the terms of the GNU Free Documentation License, Version 1.3
  or any later version published by the Free Software Foundation;
  with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
  Texts.  A copy of the license is included in the section entitled ``GNU
  Free Documentation License''.

If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the “with…Texts.” line with this:

    with the Invariant Sections being list their titles, with
    the Front-Cover Texts being list, and with the Back-Cover Texts
    being list.

If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation.

If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.

2.2.1 Making scmlit ¶

The SCM distribution Makefile contains rules for making scmlit, a “bare-bones” version of SCM sufficient for running build. build is a Scheme program used to compile (or create scripts to compile) full featured versions of SCM (see Building SCM). To create scmlit, run ‘make scmlit’ in the scm/ directory.

Makefiles are not portable to the majority of platforms. If you need to compile SCM without ‘scmlit’, there are several ways to proceed:

• Use the build web page to create custom batch scripts for compiling SCM.
• Use SCM on a different platform to run build to create a script to build SCM;
• Use another implementation of Scheme to run build to create a script to build SCM;
• Create your own script or Makefile.

Finding SLIB ¶

If you didn’t create scmlit using ‘make scmlit’, then you must create a file named scm/require.scm. For most installations, scm/require.scm can just be copied from scm/requires.scm, which is part of the SCM distribution.

If, when executing ‘scmlit’ or ‘scm’, you get a message like:

ERROR: "LOAD couldn't find file " "/usr/local/src/scm/require"

then create a file require.scm in the SCM implementation-vicinity (this is the same directory as where the file Init5f4.scm is). require.scm should have the contents:

(define (library-vicinity) "/usr/local/lib/slib/")

where the pathname string /usr/local/lib/slib/ is to be replaced by the pathname into which you unzipped (or installed) SLIB.

Alternatively, you can set the (shell) environment variable SCHEME_LIBRARY_PATH to the pathname of the SLIB directory (see Environment Variables). If set, this environment variable overrides scm/require.scm.

Absolute pathnames are recommended here; if you use a relative pathname, SLIB can get confused when the working directory is changed (see chmod). The way to specify a relative pathname is to append it to the implementation-vicinity, which is absolute:

(define library-vicinity
  (let ((lv (string-append (implementation-vicinity) "../slib/")))
    (lambda () lv)))

2.2.2 Makefile targets ¶

Each of the following four ‘make’ targets creates an executable named scm. Each target takes its build options from a file with an ‘.opt’ suffix. If that options file doesn’t exist, making that target will create the file with the ‘-F’ features: cautious, bignums, arrays, inexact, engineering-notation, and dynamic-linking. Once that ‘.opt’ file exists, you can edit it to your taste and it will be preserved.

make scm4

Produces a R4RS executable named scm lacking hygienic macros (but with defmacro). The build options are taken from scm4.opt. If build or the executable fails, try removing ‘dynamic-linking’ from scm4.opt.

make scm5

R5RS; like ‘make scm4’ but with ‘-F macro’. The build options are taken from scm5.opt. If build or the executable fails, try removing ‘dynamic-linking’ from scm5.opt.

make dscm4

Produces a R4RS executable named udscm4, which it starts and dumps to a low startup latency executable named scm. The build options are taken from udscm4.opt.

If the build fails, then ‘build scm4’ instead. If the dumped executable fails to run, then send me a bug report (and use ‘build scm4’ until the problem with dump is corrected).

make dscm5

Like ‘make dscm4’ but with ‘-F macro’. The build options are taken from udscm5.opt.

If the build fails, then ‘build scm5’ instead. If the dumped executable fails to run, then send me a bug report (and use ‘build scm5’ until the problem with dump is corrected).

If the above builds fail because of ‘-F dynamic-linking’, then (because they can’t be dynamically linked) you will likely want to add some other features to the build’s ‘.opt’ file. See the ‘-F’ build option in Build Options.

If dynamic-linking is working, then you will likely want to compile most of the modules as DLLs. The build options for compiling DLLs are in dlls.opt.

make x.so

The Xlib module; SCM Language X Interface in Xlibscm.

make myturtle

Creates a DLL named turtlegr.so which is a simple graphics API.

make wbscm.so

The wb module; B-tree database implementation in wb. Compiling this requires that wb source be in a peer directory to scm.

make dlls

Compiles all the distributed library modules, but not wbscm.so. Many of the module compiles are recursively invoked in such a way that failure of one (which could be due to a system library not being installed) doesn’t cause the top-level ‘make dlls’ to fail. If ‘make dlls’ fails as a whole, it is time to submit a bug report (see Reporting Problems).

2.3.1 Invoking Build ¶

This section teaches how to use build, a Scheme program for creating compilation scripts to produce SCM executables and library modules. The options accepted by ‘build’ are documented in Build Options.

Use the any method if you encounter problems with the other two methods (MS-DOS, Unix).

MS-DOS

From the SCM source directory, type ‘build’ followed by up to 9 command line arguments.

Unix

From the SCM source directory, type ‘./build’ followed by command line arguments.

any

From the SCM source directory, start ‘scm’ or ‘scmlit’ and type (load "build"). Alternatively, start ‘scm’ or ‘scmlit’ with the command line argument ‘-ilbuild’. This method will also work for MS-DOS and Unix.

After loading various SLIB modules, the program will print:

type (b "build <command-line>") to build
type (b*) to enter build command loop

The ‘b*’ procedure enters into a build shell where you can enter commands (with or without the ‘build’). Blank lines are ignored. To create a build script with all defaults type ‘build’.

If the build-shell encouters an error, you can reenter the build-shell by typing ‘(b*)’. To exit scm type ‘(quit)’.

Here is a transcript of an interactive (b*) build-shell.

bash$ scmlit
SCM version 5e7, Copyright (C) 1990-2006 Free Software Foundation.
SCM comes with ABSOLUTELY NO WARRANTY; for details type `(terms)'.
This is free software, and you are welcome to redistribute it
under certain conditions; type `(terms)' for details.
> (load "build")
;loading build
;  loading /home/jaffer/slib/getparam
;    loading /home/jaffer/slib/coerce
...
;  done loading build.scm
type (b "build <command-line>") to build
type (b*) to enter build command loop
;done loading build
#<unspecified>
> (b*)
;loading /home/jaffer/slib/comparse
;done loading /home/jaffer/slib/comparse.scm
build> -t exe
#! /bin/sh
# unix (linux) script created by SLIB/batch Wed Oct 26 17:14:23 2011
# [-p linux]
# ================ Write file with C defines
rm -f scmflags.h
echo '#define IMPLINIT "Init5e7.scm"'>>scmflags.h
echo '#define BIGNUMS'>>scmflags.h
echo '#define FLOATS'>>scmflags.h
echo '#define ARRAYS'>>scmflags.h
# ================ Compile C source files
gcc -c continue.c scm.c scmmain.c findexec.c script.c time.c repl.c scl.c eval.c sys.c subr.c debug.c unif.c rope.c
# ================ Link C object files
gcc -rdynamic -o scm continue.o scm.o scmmain.o findexec.o script.o time.o repl.o scl.o eval.o sys.o subr.o debug.o unif.o rope.o -lm -lc
"scm"
build> -t exe -w myscript.sh
"scm"
build> (quit)

No compilation was done. The ‘-t exe’ command shows the compile script. The ‘-t exe -w myscript.sh’ line creates a file myscript.sh containing the compile script. To actually compile and link it, type ‘./myscript.sh’.

Invoking build without the ‘-F’ option will build or create a shell script with the arrays, inexact, and bignums options as defaults. Invoking ‘build’ with ‘-F lit -o scmlit’ will make a script for compiling ‘scmlit’.

bash$ ./build
-|
#! /bin/sh
# unix (linux) script created by SLIB/batch 
# ================ Write file with C defines
rm -f scmflags.h
echo '#define IMPLINIT "Init5f4.scm"'>>scmflags.h
echo '#define BIGNUMS'>>scmflags.h
echo '#define FLOATS'>>scmflags.h
echo '#define ARRAYS'>>scmflags.h
# ================ Compile C source files
gcc -O2 -c continue.c scm.c scmmain.c findexec.c script.c time.c repl.c scl.c eval.c sys.c subr.c debug.c unif.c rope.c
# ================ Link C object files
gcc -rdynamic -o scm continue.o scm.o scmmain.o findexec.o script.o time.o repl.o scl.o eval.o sys.o subr.o debug.o unif.o rope.o -lm -lc

To cross compile for another platform, invoke build with the ‘-p’ or ‘--platform=’ option. This will create a script for the platform named in the ‘-p’ or ‘--platform=’ option.

bash$ ./build -o scmlit -p darwin -F lit
-|
#! /bin/sh
# unix (darwin) script created by SLIB/batch 
# ================ Write file with C defines
rm -f scmflags.h
echo '#define IMPLINIT "Init5f4.scm"'>>scmflags.h
# ================ Compile C source files
cc -O3 -c continue.c scm.c scmmain.c findexec.c script.c time.c repl.c scl.c eval.c sys.c subr.c debug.c unif.c rope.c
# ================ Link C object files
mv -f scmlit scmlit~
cc -o scmlit continue.o scm.o scmmain.o findexec.o script.o time.o repl.o scl.o eval.o sys.o subr.o debug.o unif.o rope.o

2.3.2 Build Options ¶

The options to build specify what, where, and how to build a SCM program or dynamically linked module. These options are unrelated to the SCM command line options.

Build Option: -p platform-name ¶

Build Option: ---platform=platform-name ¶

specifies that the compilation should be for a computer/operating-system combination called platform-name. Note The case of platform-name is distinguised. The current platform-names are all lower-case.

The platforms defined by table platform in build.scm are:

Table: platform
name              processor         operating-system  compiler          
#f                processor-family  operating-system  #f                
symbol            processor-family  operating-system  symbol            
symbol            symbol            symbol            symbol            
================= ================= ================= ================= 
*unknown*         *unknown*         unix              cc                
acorn-unixlib     acorn             *unknown*         cc                
aix               powerpc           aix               cc                
alpha-elf         alpha             unix              cc                
alpha-linux       alpha             linux             gcc               
amiga-aztec       m68000            amiga             cc                
amiga-dice-c      m68000            amiga             dcc               
amiga-gcc         m68000            amiga             gcc               
amiga-sas         m68000            amiga             lc                
atari-st-gcc      m68000            atari-st          gcc               
atari-st-turbo-c  m68000            atari-st          tcc               
borland-c         i8086             ms-dos            bcc               
darwin            powerpc           unix              cc                
djgpp             i386              ms-dos            gcc               
freebsd           *unknown*         unix              cc                
gcc               *unknown*         unix              gcc               
gnu-win32         i386              unix              gcc               
highc             i386              ms-dos            hc386             
hp-ux             hp-risc           hp-ux             cc                
irix              mips              irix              gcc               
linux             *unknown*         linux             gcc               
linux-aout        i386              linux             gcc               
linux-ia64        ia64              linux             gcc               
microsoft-c       i8086             ms-dos            cl                
microsoft-c-nt    i386              ms-dos            cl                
microsoft-quick-c i8086             ms-dos            qcl               
ms-dos            i8086             ms-dos            cc                
netbsd            *unknown*         unix              gcc               
openbsd           *unknown*         unix              gcc               
os/2-cset         i386              os/2              icc               
os/2-emx          i386              os/2              gcc               
osf1              alpha             unix              cc                
plan9-8           i386              plan9             8c                
sunos             sparc             sunos             cc                
svr4              *unknown*         unix              cc                
svr4-gcc-sun-ld   sparc             sunos             gcc               
turbo-c           i8086             ms-dos            tcc               
unicos            cray              unicos            cc                
unix              *unknown*         unix              cc                
vms               vax               vms               cc                
vms-gcc           vax               vms               gcc               
watcom-9.0        i386              ms-dos            wcc386p           

Build Option: -f pathname ¶

specifies that the build options contained in pathname be spliced into the argument list at this point. The use of option files can separate functional features from platform-specific ones.

The Makefile calls out builds with the options in ‘.opt’ files:

dlls.opt

Options for Makefile targets dlls, myturtle, and x.so.

gdb.opt

Options for udgdbscm and gdbscm.

libscm.opt

Options for libscm.a.

pg.opt

Options for pgscm, which instruments C functions.

udscm4.opt

Options for targets udscm4 and dscm4 (scm).

udscm5.opt

Options for targets udscm5 and dscm5 (scm).

The Makefile creates options files it depends on only if they do not already exist.

Build Option: -o filename ¶

Build Option: ---outname=filename ¶

specifies that the compilation should produce an executable or object name of filename. The default is ‘scm’. Executable suffixes will be added if neccessary, e.g. ‘scm’ ⇒ ‘scm.exe’.

Build Option: -l libname … ¶

Build Option: ---libraries=libname ¶

specifies that the libname should be linked with the executable produced. If compile flags or include directories (‘-I’) are needed, they are automatically supplied for compilations. The ‘c’ library is always included. SCM features specify any libraries they need; so you shouldn’t need this option often.

Build Option: -D definition … ¶

Build Option: ---defines=definition ¶

specifies that the definition should be made in any C source compilations. If compile flags or include directories (‘-I’) are needed, they are automatically supplied for compilations. SCM features specify any flags they need; so you shouldn’t need this option often.

Build Option: ---compiler-options=flag ¶

specifies that that flag will be put on compiler command-lines.

Build Option: ---linker-options=flag ¶

specifies that that flag will be put on linker command-lines.

Build Option: -s pathname ¶

Build Option: ---scheme-initial=pathname ¶

specifies that pathname should be the default location of the SCM initialization file Init5f4.scm. SCM tries several likely locations before resorting to pathname (see File-System Habitat). If not specified, the current directory (where build is building) is used.

Build Option: -c pathname … ¶

Build Option: ---c-source-files=pathname ¶

specifies that the C source files pathname … are to be compiled.

Build Option: -j pathname … ¶

Build Option: ---object-files=pathname ¶

specifies that the object files pathname … are to be linked.

Build Option: -i call … ¶

Build Option: ---initialization=call ¶

specifies that the C functions call … are to be invoked during initialization.

Build Option: -t build-what ¶

Build Option: ---type=build-what ¶

specifies in general terms what sort of thing to build. The choices are:

‘exe’

executable program.

‘lib’

library module.

‘dlls’

archived dynamically linked library object files.

‘dll’

dynamically linked library object file.

The default is to build an executable.

Build Option: -h batch-syntax ¶

Build Option: --batch-dialect=batch-syntax ¶

specifies how to build. The default is to create a batch file for the host system. The SLIB file batch.scm knows how to create batch files for:

• unix
• dos
• vms
• amigaos (was amigados)
• system

  This option executes the compilation and linking commands through the use of the system procedure.

• *unknown*

  This option outputs Scheme code.

Build Option: -w batch-filename ¶

Build Option: --script-name=batch-filename ¶

specifies where to write the build script. The default is to display it on (current-output-port).

Build Option: -F feature … ¶

Build Option: ---features=feature ¶

specifies to build the given features into the executable. The defined features are:

array ¶

Alias for ARRAYS

array-for-each ¶

array-map! and array-for-each (arrays must also be featured).

arrays ¶

Use if you want arrays, uniform-arrays and uniform-vectors.

bignums ¶

Large precision integers.

byte ¶

Treating strings as byte-vectors.

byte-number ¶

Byte/number conversions

careful-interrupt-masking ¶

Define this for extra checking of interrupt masking and some simple checks for proper use of malloc and free. This is for debugging C code in sys.c, eval.c, repl.c and makes the interpreter several times slower than usual.

cautious ¶

Normally, the number of arguments arguments to interpreted closures (from LAMBDA) are checked if the function part of a form is not a symbol or only the first time the form is executed if the function part is a symbol. defining ‘reckless’ disables any checking. If you want to have SCM always check the number of arguments to interpreted closures define feature ‘cautious’.

cheap-continuations ¶

If you only need straight stack continuations, executables compile with this feature will run faster and use less storage than not having it. Machines with unusual stacks need this. Also, if you incorporate new C code into scm which uses VMS system services or library routines (which need to unwind the stack in an ordrly manner) you may need to use this feature.

compiled-closure ¶

Use if you want to use compiled closures.

curses ¶

For the curses screen management package.

debug ¶

Turns on the features ‘cautious’ and ‘careful-interrupt-masking’; uses -g flags for debugging SCM source code.

differ ¶

Sequence comparison

dont-memoize-locals ¶

SCM normally converts references to local variables to ILOCs, which make programs run faster. If SCM is badly broken, try using this option to disable the MEMOIZE_LOCALS feature.

dump ¶

Convert a running scheme program into an executable file.

dynamic-linking ¶

Be able to load compiled files while running.

edit-line ¶

interface to the editline or GNU readline library.

engineering-notation ¶

Use if you want floats to display in engineering notation (exponents always multiples of 3) instead of scientific notation.

generalized-c-arguments ¶

make_gsubr for arbitrary (< 11) arguments to C functions.

i/o-extensions ¶

Commonly available I/O extensions: exec, line I/O, file positioning, file delete and rename, and directory functions.

inexact ¶

Use if you want floating point numbers.

lit ¶

Lightweight – no features

macro ¶

C level support for hygienic and referentially transparent macros (syntax-rules macros).

mysql ¶

Client connections to the mysql databases.

no-heap-shrink ¶

Use if you want segments of unused heap to not be freed up after garbage collection. This may increase time in GC for *very* large working sets.

none ¶

No features

posix ¶

Posix functions available on all Unix-like systems. fork and process functions, user and group IDs, file permissions, and link.

reckless ¶

If your scheme code runs without any errors you can disable almost all error checking by compiling all files with ‘reckless’.

record ¶

The Record package provides a facility for user to define their own record data types. See SLIB for documentation.

regex ¶

String regular expression matching.

rev2-procedures ¶

These procedures were specified in the Revised^2 Report on Scheme but not in R4RS.

sicp ¶

Use if you want to run code from:

Harold Abelson and Gerald Jay Sussman with Julie Sussman. Structure and Interpretation of Computer Programs. The MIT Press, Cambridge, Massachusetts, USA, 1985.

Differences from R5RS are:

• (eq? ’() ’#f)
• (define a 25) returns the symbol a.
• (set! a 36) returns 36.

single-precision-only ¶

Use if you want all inexact real numbers to be single precision. This only has an effect if SINGLES is also defined (which is the default). This does not affect complex numbers.

socket ¶

BSD socket interface. Socket addr functions require inexacts or bignums for 32-bit precision.

tick-interrupts ¶

Use if you want the ticks and ticks-interrupt functions.

turtlegr ¶

Turtle graphics calls for both Borland-C and X11 from sjm@ee.tut.fi.

unix ¶

Those unix features which have not made it into the Posix specs: nice, acct, lstat, readlink, symlink, mknod and sync.

wb ¶

WB database with relational wrapper.

wb-no-threads ¶

no-comment

windows ¶

Microsoft Windows executable.

x ¶

Alias for Xlib feature.

xlib ¶

Interface to Xlib graphics routines.

2.3.3 Compiling and Linking Custom Files ¶

A correspondent asks:

How can we link in our own c files to the SCM interpreter so that we can add our own functionality? (e.g. we have a bunch of tcp functions we want access to). Would this involve changing build.scm or the Makefile or both?

(see Changing Scm has instructions describing the C code format). Suppose a C file foo.c has functions you wish to add to SCM. To compile and link your file at compile time, use the ‘-c’ and ‘-i’ options to build:

bash$ ./build -c foo.c -i init_foo
-|
#! /bin/sh
rm -f scmflags.h
echo '#define IMPLINIT "/home/jaffer/scm/Init5f4.scm"'>>scmflags.h
echo '#define COMPILED_INITS init_foo();'>>scmflags.h
echo '#define BIGNUMS'>>scmflags.h
echo '#define FLOATS'>>scmflags.h
echo '#define ARRAYS'>>scmflags.h
gcc -O2 -c continue.c scm.c findexec.c script.c time.c repl.c scl.c \
        eval.c sys.c subr.c unif.c rope.c foo.c
gcc -rdynamic -o scm continue.o scm.o findexec.o script.o time.o \
        repl.o scl.o eval.o sys.o subr.o unif.o rope.o foo.o -lm -lc

To make a dynamically loadable object file use the -t dll option:

bash$ ./build -t dll -c foo.c
-|
#! /bin/sh
rm -f scmflags.h
echo '#define IMPLINIT "/home/jaffer/scm/Init5f4.scm"'>>scmflags.h
echo '#define BIGNUMS'>>scmflags.h
echo '#define FLOATS'>>scmflags.h
echo '#define ARRAYS'>>scmflags.h
echo '#define DLL'>>scmflags.h
gcc -O2 -fpic -c foo.c
gcc -shared -o foo.so foo.o -lm -lc

Once foo.c compiles correctly (and your SCM build supports dynamic-loading), you can load the compiled file with the Scheme command (load "./foo.so"). See Configure Module Catalog for how to add a compiled dll file to SLIB’s catalog.

2.6.1 Problems Compiling ¶

2.6.2 Problems Linking ¶

2.6.3 Testing ¶

Loading r4rstest.scm in the distribution will run an [R4RS] conformance test on scm.

> (load "r4rstest.scm")
-|
;loading r4rstest.scm
SECTION(2 1)
SECTION(3 4)
 #<primitive-procedure boolean?>
    #<primitive-procedure char?>
       #<primitive-procedure null?>
          #<primitive-procedure number?>
...

Loading pi.scm in the distribution will enable you to compute digits of pi.

> (load "pi.scm")
;loading pi.scm
;done loading pi.scm
#<unspecified>
> (pi 100 5)
00003 14159 26535 89793 23846 26433 83279 50288 41971 69399
37510 58209 74944 59230 78164 06286 20899 86280 34825 34211
70679
;Evaluation took 550 ms (60 in gc) 36976 cells work, 1548.B other
#<unspecified>

Performance ¶

Loading bench.scm will compute and display performance statistics of SCM running pi.scm. ‘make bench’ or ‘make benchlit’ appends the performance report to the file BenchLog, facilitating tracking effects of changes to SCM on performance.

2.6.4 Problems Starting ¶

2.6.5 Problems Running ¶

2.6.6 Reporting Problems ¶

Reported problems and solutions are grouped under Compiling, Linking, Running, and Testing. If you don’t find your problem listed there, you can send a bug report to agj@alum.mit.edu or scm-discuss@gnu.org. The bug report should include:

1. The version of SCM (printed when SCM is invoked with no arguments).
2. The type of computer you are using.
3. The name and version of your computer’s operating system.
4. The values of the environment variables SCM_INIT_PATH and SCHEME_LIBRARY_PATH.
5. The name and version of your C compiler.
6. If you are using an executable from a distribution, the name, vendor, and date of that distribution. In this case, corresponding with the vendor is recommended.

3.12.1 Executable path ¶

In order to dump a saved executable or to dynamically-link using DLD, SCM must know where its executable file is. Sometimes SCM (see Executable Pathname) guesses incorrectly the location of the currently running executable. In that case, the correct path can be set by calling execpath with the pathname.

Function: execpath ¶

Returns the path (string) which SCM uses to find the executable file whose invocation the currently running session is, or #f if the path is not set.

Function: execpath #f ¶

Function: execpath newpath ¶

Sets the path to #f or newpath, respectively. The old path is returned.

For other configuration constants and procedures See Configuration in SLIB.

3.13.1 Unix Scheme Scripts ¶

In reading this section, keep in mind that the first line of a script file has (different) meanings to SCM and the operating system (execve).

file: #! interpreter \ … ¶

On unix systems, a Shell-Script is a file (with execute permissions) whose first two characters are ‘#!’. The interpreter argument must be the pathname of the program to process the rest of the file. The directories named by environment variable PATH are not searched to find interpreter.

When executing a shell-script, the operating system invokes interpreter with a single argument encapsulating the rest of the first line’s contents (if not just whitespace), the pathname of the Scheme Script file, and then any arguments which the shell-script was invoked with.

Put one space character between ‘#!’ and the first character of interpreter (‘/’). The interpreter name is followed by ‘ \’; SCM substitutes the second line of file for ‘\’ (and the rest of the line), then appends any arguments given on the command line invoking this Scheme-Script.

When SCM executes the script, the Scheme variable *script* will be set to the script pathname. The last argument before ‘!#’ on the second line should be ‘-’; SCM will load the script file, preserve the unprocessed arguments, and set *argv* to a list of the script pathname and the unprocessed arguments.

Note that the interpreter, not the operating system, provides the ‘\’ substitution; this will only take place if interpreter is a SCM or SCSH interpreter.

Read syntax: #! ignored !# ¶

When the first two characters of the file being loaded are #! and a ‘\’ is present before a newline in the file, all characters up to ‘!#’ will be ignored by SCM read.

This combination of interpretatons allows SCM source files to be used as POSIX shell-scripts if the first line is:

#! /usr/bin/scm \

The following Scheme-Script prints factorial of its argument:

#! /usr/bin/scm \ %0 %*
- !#

(define (fact.script args)
  (cond ((and (= 1 (length args))
              (string->number (car args)))
         => (lambda (n) (print (fact n)) #t))
        (else (fact.usage))))

(define (fact.usage)
  (print *argv*)
  (display "\
Usage: fact N
  Returns the factorial of N.
"
           (current-error-port))
  #f)

(define (fact n) (if (< n 2) 1 (* n (fact (+ -1 n)))))

(if *script* (exit (fact.script (list-tail *argv* *optind*))))

./fact 32
⇒
263130836933693530167218012160000000

If the wrong number of arguments is given, fact prints its argv with usage information.

./fact 3 2
-|
("./fact" "3" "2") 
Usage: fact N
  Returns the factorial of N.

3.13.2 MS-DOS Compatible Scripts ¶

It turns out that we can create scheme-scripts which run both under unix and MS-DOS. To implement this, I have written the MS-DOS programs: #!.bat and !#.exe, which are available from: http://groups.csail.mit.edu/mac/ftpdir/scm/sharpbang.zip

With these two programs installed in a PATH directory, we have the following syntax for <program>.BAT files.

file: #! interpreter \ %0 %* ¶

The first two characters of the Scheme-Script are ‘#!’. The interpreter can be either a unix style program path (using ‘/’ between filename components) or a DOS program name or path. The rest of the first line of the Scheme-Script should be literally ‘\ %0 %*’, as shown.

If interpreter has ‘/’ in it, interpreter is converted to a DOS style filename (‘/’ ⇒ ‘\’).

In looking for an executable named interpreter, #! first checks this (converted) filename; if interpreter doesn’t exist, it then tries to find a program named like the string starting after the last ‘\’ (or ‘/’) in interpreter. When searching for executables, #! tries all directories named by environment variable PATH.

Once the interpreter executable path is found, arguments are processed in the manner of scheme-shell, with all the text after the ‘\’ taken as part of the meta-argument. More precisely, #! calls interpreter with any options on the second line of the Scheme-Script up to ‘!#’, the name of the Scheme-Script file, and then any of at most 8 arguments given on the command line invoking this Scheme-Script.

The previous example Scheme-Script works in both MS-DOS and unix systems.

3.13.3 Unix Shell Scripts ¶

Scheme-scripts suffer from two drawbacks:

• Some Unixes limit the length of the ‘#!’ interpreter line to the size of an object file header, which can be as small as 32 bytes.
• A full, explicit pathname must be specified, perhaps requiring more than 32 bytes and making scripts vulnerable to breakage when programs are moved.

The following approach solves these problems at the expense of slower startup. Make ‘#! /bin/sh’ the first line and prepend every subsequent line to be executed by the shell with :;. The last line to be executed by the shell should contain an exec command; exec tail-calls its argument.

/bin/sh is thus invoked with the name of the script file, which it executes as a *sh script. Usually the second line starts ‘:;exec scm -f$0’, which executes scm, which in turn loads the script file. When SCM loads the script file, it ignores the first and second lines, and evaluates the rest of the file as Scheme source code.

The second line of the script file does not have the length restriction mentioned above. Also, /bin/sh searches the directories listed in the ‘PATH’ environment variable for ‘scm’, eliminating the need to use absolute locations in order to invoke a program.

The following example additionally sets *script* to the script argument, making it compatible with the scheme code of the previous example.

#! /bin/sh
:;exec scm -e"(set! *script* \"$0\")" -l$0 "$@"

(define (fact.script args)
  (cond ((and (= 1 (length args))
              (string->number (car args)))
         => (lambda (n) (print (fact n)) #t))
        (else (fact.usage))))

(define (fact.usage)
  (print *argv*)
  (display "\
Usage: fact N
  Returns the factorial of N.
"
           (current-error-port))
  #f)

(define (fact n) (if (< n 2) 1 (* n (fact (+ -1 n)))))

(if *script* (exit (fact.script (list-tail *argv* *optind*))))

./fact 6
⇒ 720 

4.6.1 Opening and Closing ¶

Function: open-file string modes ¶

Function: try-open-file string modes ¶

Returns a port capable of receiving or delivering characters as specified by the modes string. If a file cannot be opened #f is returned.

Internal functions opening files callback to the SCM function open-file. You can extend open-file by redefining it. try-open-file is the primitive procedure; Do not redefine try-open-file!

Constant: open_read ¶

Constant: open_write ¶

Constant: open_both ¶

Contain modes strings specifying that a file is to be opened for reading, writing, and both reading and writing respectively.

Both input and output functions can be used with io-ports. An end of file must be read or a two-argument file-position done on the port between a read operation and a write operation or vice-versa.

Function: _ionbf modestr ¶

Returns a version of modestr which when open-file is called with it as the second argument will return an unbuffered port. An input-port must be unbuffered in order for char-ready? and wait-for-input to work correctly on it. The initial value of (current-input-port) is unbuffered if the platform supports it.

Function: _tracked modestr ¶

Returns a version of modestr which when open-file is called with it as the second argument will return a tracked port. A tracked port maintains current line and column numbers, which may be queried with port-line and port-column.

Function: _exclusive modestr ¶

Returns a version of modestr which when open-file is called with it as the second argument will return a port only if the named file does not already exist. This functionality is provided by calling try-create-file See I/O-Extensions, which is not available for all platforms.

Function: open-ports ¶

Returns a list of all currently open ports, excluding string ports, see See String Ports in SLIB. This may be useful after a fork See Posix Extensions, or for debugging. Bear in mind that ports that would be closed by gc will be kept open by a reference to this list.

Function: close-port port ¶

Closes port. The same as close-input-port and close-output-port.

4.6.2 Port Properties ¶

Function: port-closed? port ¶

Returns #t if port is closed.

Function: port-type obj ¶

If obj is not a port returns false, otherwise returns a symbol describing the port type, for example string or pipe.

Function: port-filename port ¶

Returns the filename port was opened with. If port is not open to a file the result is unspecified.

Function: file-position port ¶

Function: file-position port #f ¶

Returns the current position of the character in port which will next be read or written. If port is open to a non-file then #f is returned.

Function: file-position port k ¶

Sets the current position in port which will next be read or written. If successful, #f is returned. If port is open to a non-file, then file-position returns #f.

Function: port-line port ¶

Function: port-column port ¶

If port is a tracked port, return the current line (column) number, otherwise return #f. Line and column numbers begin with 1. The column number applies to the next character to be read; if that character is a newline, then the column number will be one more than the length of the line.

Function: freshline port ¶

Outputs a newline to optional argument port unless the current output column number of port is known to be zero, ie output will start at the beginning of a new line. port defaults to current-output-port. If port is not a tracked port freshline is equivalent to newline.

Function: isatty? port ¶

Returns #t if port is input or output to a serial non-file device.

procedure: char-ready? ¶

procedure: char-ready? port ¶

Returns #t if a character is ready on the input port and returns #f otherwise. If char-ready? returns #t then the next read-char operation on the given port is guaranteed not to hang. If the port is at end of file then char-ready? returns #t. Port may be omitted, in which case it defaults to the value returned by current-input-port.

Rationale Char-ready? exists to make it possible for a program to accept characters from interactive ports without getting stuck waiting for input. Any input editors associated with such ports must ensure that characters whose existence has been asserted by char-ready? cannot be rubbed out. If char-ready? were to return #f at end of file, a port at end of file would be indistinguishable from an interactive port that has no ready characters.

procedure: wait-for-input x ¶

procedure: wait-for-input x port1 … ¶

Returns a list those ports port1 … which are char-ready?. If none of port1 … become char-ready? within the time interval of x seconds, then #f is returned. The port1 … arguments may be omitted, in which case they default to the list of the value returned by current-input-port.

4.6.3 Port Redirection ¶

Function: current-error-port ¶

Returns the current port to which diagnostic output is directed.

Function: with-error-to-file string thunk ¶

thunk must be a procedure of no arguments, and string must be a string naming a file. The file is opened for output, an output port connected to it is made the default value returned by current-error-port, and the thunk is called with no arguments. When the thunk returns, the port is closed and the previous default is restored. With-error-to-file returns the value yielded by thunk.

Function: with-input-from-port port thunk ¶

Function: with-output-to-port port thunk ¶

Function: with-error-to-port port thunk ¶

These routines differ from with-input-from-file, with-output-to-file, and with-error-to-file in that the first argument is a port, rather than a string naming a file.

Function: call-with-outputs thunk proc ¶

Calls the thunk procedure while the current-output-port and current-error-port are directed to string-ports. If thunk returns, the proc procedure is called with the output-string, the error-string, and the value returned by thunk. If thunk does not return a value (perhaps because of error), proc is called with just the output-string and the error-string as arguments.

4.6.4 Soft Ports ¶

A soft-port is a port based on a vector of procedures capable of accepting or delivering characters. It allows emulation of I/O ports.

Function: make-soft-port vector modes ¶

Returns a port capable of receiving or delivering characters as specified by the modes string (see open-file). vector must be a vector of length 5. Its components are as follows:

0. procedure accepting one character for output
1. procedure accepting a string for output
2. thunk for flushing output
3. thunk for getting one character
4. thunk for closing port (not by garbage collection)

For an output-only port only elements 0, 1, 2, and 4 need be procedures. For an input-only port only elements 3 and 4 need be procedures. Thunks 2 and 4 can instead be #f if there is no useful operation for them to perform.

If thunk 3 returns #f or an eof-object (see eof-object? in Revised(5) Scheme) it indicates that the port has reached end-of-file. For example:

If it is necessary to explicitly close the port when it is garbage collected, (see add-finalizer).

(define stdout (current-output-port))
(define p (make-soft-port
           (vector
            (lambda (c) (write c stdout))
            (lambda (s) (display s stdout))
            (lambda () (display "." stdout))
            (lambda () (char-upcase (read-char)))
            (lambda () (display "@" stdout)))
           "rw"))

(write p p) ⇒ #<input-output-soft#\space45d10#\>

4.7.1 Line Numbers ¶

Scheme code defined by load may optionally contain line number information. Currently this information is used only for reporting expansion time errors, but in the future run-time error messages may also include line number information.

Function: try-load pathname reader ¶

This is the primitive for loading, pathname is the name of a file containing Scheme code, and optional argument reader is a function of one argument, a port. reader should read and return Scheme code as list structure. The default value is read, which is used if reader is not supplied or is false.

Line number objects are disjoint from integers or other Scheme types. When evaluated or loaded as Scheme code, an s-expression containing a line-number in the car is equivalent to the cdr of the s-expression. A pair consisting of a line-number in the car and a vector in the cdr is equivalent to the vector. The meaning of s-expressions with line-numbers in other positions is undefined.

Function: read-numbered port ¶

Behaves like read, except that

• Load (read) sytnaxes are enabled.
• every s-expression read will be replaced with a cons of a line-number object and the sexp actually read. This replacement is done only if port is a tracked port See See Files and Ports.

Function: integer->line-number int ¶

Returns a line-number object with value int. int should be an exact non-negative integer.

Function: line-number->integer linum ¶

Returns the value of line-number object linum as an integer.

Function: line-number? obj ¶

Returns true if and only if obj is a line-number object.

Function: read-for-load port ¶

Behaves like read, except that load syntaxes are enabled.

Variable: *load-reader* ¶

Variable: *slib-load-reader* ¶

The value of *load-reader* should be a value acceptable as the second argument to try-load (note that #f is acceptable). This value will be used to read code during calls to scm:load. The value of *slib-load-reader* will similarly be used during calls to slib:load and require.

In order to disable all line-numbering, it is sufficient to set! *load-reader* and *slib-load-reader* to #f.

4.8.1 Common-Lisp Read Syntax ¶

Read syntax: #\token ¶

If token is a sequence of two or more digits, then this syntax is equivalent to #.(integer->char (string->number token 8)).

If token is C-, c-, or ^ followed by a character, then this syntax is read as a control character. If token is M- or m- followed by a character, then a meta character is read. c- and m- prefixes may be combined.

Read syntax: #+ feature form ¶

If feature is provided? then form is read as a scheme expression. If not, then form is treated as whitespace.

Feature is a boolean expression composed of symbols and and, or, and not of boolean expressions.

For more information on provided?, See Require in SLIB.

Read syntax: #- feature form ¶

is equivalent to #+(not feature) expression.

Read syntax: #| any thing |# ¶

Is a balanced comment. Everything up to the matching |# is ignored by the read. Nested #|…|# can occur inside any thing.

Load sytax is Read syntax enabled for read only when that read is part of loading a file or string. This distinction was made so that reading from a datafile would not be able to corrupt a scheme program using ‘#.’.

Load syntax: #. expression ¶

Is read as the object resulting from the evaluation of expression. This substitution occurs even inside quoted structure.

In order to allow compiled code to work with #. it is good practice to define those symbols used inside of expression with #.(define …). For example:

#.(define foo 9)                        ⇒ #<unspecified>
'(#.foo #.(+ foo foo))                  ⇒ (9 18)

Load syntax: #' form ¶

is equivalent to form (for compatibility with common-lisp).

4.8.2 Load Syntax ¶

#! is the unix mechanism for executing scripts. See Unix Scheme Scripts for the full description of how this comment supports scripting.

Load syntax: #?line ¶

Load syntax: #?column ¶

Return integers for the current line and column being read during a load.

Load syntax: #?file ¶

Returns the string naming the file currently being loaded. This path is the string passed to load, possibly with ‘.scm’ appended.

4.8.3 Documentation and Comments ¶

procedure: procedure-documentation proc ¶

Returns the documentation string of proc if it exists, or #f if not.

If the body of a lambda (or the definition of a procedure) has more than one expression, and the first expression (preceeding any internal definitions) is a string, then that string is the documentation string of that procedure.

(procedure-documentation (lambda (x) "Identity" x)) ⇒ "Identity"
(define (square x)
    "Return the square of X."
    (* x x))
⇒ #<unspecified>
(procedure-documentation square) ⇒ "Return the square of X."

Function: comment string1 … ¶

Appends string1 … to the strings given as arguments to previous calls comment.

Function: comment ¶

Returns the (appended) strings given as arguments to previous calls comment and empties the current string collection.

Load syntax: #;text-till-end-of-line ¶

Behaves as (comment "text-till-end-of-line").

4.8.4 Modifying Read Syntax ¶

Callback procedure: read:sharp c port ¶

If a # followed by a character (for a non-standard syntax) is encountered by read, read will call the value of the symbol read:sharp with arguments the character and the port being read from. The value returned by this function will be the value of read for this expression unless the function returns #<unspecified> in which case the expression will be treated as whitespace. #<unspecified> is the value returned by the expression (if #f #f).

Callback procedure: load:sharp c port ¶

Dispatches like read:sharp, but only during loads. The read-syntaxes handled by load:sharp are a superset of those handled by read:sharp. load:sharp calls read:sharp if none of its syntaxes match c.

Callback procedure: char:sharp token ¶

If the sequence #\ followed by a non-standard character name is encountered by read, read will call the value of the symbol char:sharp with the token (a string of length at least two) as argument. If the value returned is a character, then that will be the value of read for this expression, otherwise an error will be signaled.

Note When adding new # syntaxes, have your code save the previous value of load:sharp, read:sharp, or char:sharp when defining it. Call this saved value if an invocation’s syntax is not recognized. This will allow #+, #-, and Uniform Arrays to still be supported (as they dispatch from read:sharp).

4.9.1 Define and Set ¶

Special Form: defined? symbol ¶

Equivalent to #t if symbol is a syntactic keyword (such as if) or a symbol with a value in the top level environment (see Variables and regions in Revised(5) Scheme). Otherwise equivalent to #f.

Special Form: defvar identifier initial-value ¶

If identifier is unbound in the top level environment, then identifier is defined to the result of evaluating the form initial-value as if the defvar form were instead the form (define identifier initial-value) . If identifier already has a value, then initial-value is not evaluated and identifier’s value is not changed. defvar is valid only when used at top-level.

Special Form: defconst identifier value ¶

If identifier is unbound in the top level environment, then identifier is defined to the result of evaluating the form value as if the defconst form were instead the form (define identifier value) . If identifier already has a value, then value is not evaluated, identifier’s value is not changed, and an error is signaled. defconst is valid only when used at top-level.

Special Form: set! (variable1 variable2 …) <expression> ¶

The identifiers variable1, variable2, … must be bound either in some region enclosing the ‘set!’ expression or at top level.

<Expression> is evaluated, and the elements of the resulting list are stored in the locations to which each corresponding variable is bound. The result of the ‘set!’ expression is unspecified.

(define x 2)
(define y 3)
(+ x y)                              ⇒ 5
(set! (x y) (list 4 5))              ⇒ unspecified
(+ x y)                              ⇒ 9

Special Form: qase key clause1 clause2 … ¶

qase is an extension of standard Scheme case: Each clause of a qase statement must have as first element a list containing elements which are:

• literal datums, or
• a comma followed by the name of a symbolic constant, or
• a comma followed by an at-sign (@) followed by the name of a symbolic constant whose value is a list.

A qase statement is equivalent to a case statement in which these symbolic constants preceded by commas have been replaced by the values of the constants, and all symbolic constants preceded by comma-at-signs have been replaced by the elements of the list values of the constants. This use of comma, (or, equivalently, unquote) is similar to that of quasiquote except that the unquoted expressions must be symbolic constants.

Symbolic constants are defined using defconst, their values are substituted in the head of each qase clause during macro expansion. defconst constants should be defined before use. qase can be substituted for any correct use of case.

(defconst unit '1)
(defconst semivowels '(w y))
(qase (* 2 3)
  ((2 3 5 7) 'prime)
  ((,unit 4 6 8 9) 'composite))        ==>  composite
(qase (car '(c d))
  ((a) 'a)
  ((b) 'b))                            ==>  unspecified
(qase (car '(c d))
  ((a e i o u) 'vowel)
  ((,@semivowels) 'semivowel)
  (else 'consonant))                   ==>  consonant

4.9.2 Defmacro ¶

SCM supports the following constructs from Common Lisp: defmacro, macroexpand, macroexpand-1, and gentemp. See Defmacro in SLIB.

SCM defmacro is extended over that described for SLIB:

(defmacro (macro-name . arguments) body)

is equivalent to

(defmacro macro-name arguments body)

As in Common Lisp, an element of the formal argument list for defmacro may be a possibly nested list, in which case the corresponding actual argument must be a list with as many members as the formal argument. Rest arguments are indicated by improper lists, as in Scheme. It is an error if the actual argument list does not have the tree structure required by the formal argument list.

For example:

(defmacro (let1 ((name value)) . body)
    `((lambda (,name) ,@body) ,value))

(let1 ((x (foo))) (print x) x) ≡ ((lambda (x) (print x) x) (foo))

(let1 not legal syntax) error→ not "does not match" ((name value))

4.9.3 Syntax-Rules ¶

SCM supports [R5RS] syntax-rules macros See Macros in Revised(5) Scheme.

The pattern language is extended by the syntax (... <obj>), which is identical to <obj> except that ellipses in <obj> are treated as ordinary identifiers in a template, or as literals in a pattern. In particular, (... ...) quotes the ellipsis token ... in a pattern or template.

For example:

(define-syntax check-tree
  (syntax-rules ()
    ((_ (?pattern (... ...)) ?obj)
     (let loop ((obj ?obj))
       (or (null? obj)
           (and (pair? obj)
                (check-tree ?pattern (car obj))
                (loop (cdr obj))))))
    ((_ (?first . ?rest) ?obj)
     (let ((obj ?obj))
       (and (pair? obj)
            (check-tree ?first (car obj))
            (check-tree ?rest (cdr obj)))))
    ((_ ?atom ?obj) #t)))

(check-tree ((a b) ...) '((1 2) (3 4) (5 6))) ⇒ #t

(check-tree ((a b) ...) '((1 2) (3 4) not-a-2list) ⇒ #f

Note that although the ellipsis is matched as a literal token in the defined macro it is not included in the literals list for syntax-rules.

The pattern language is also extended to support identifier macros. A reference to an identifier macro keyword that is not the first identifier in a form may expand into Scheme code, rather than raising a “keyword as variable” error. The pattern for expansion of such a bare macro keyword is a single identifier, as in other syntax rules the identifier is ignored.

For example:

(define-syntax eight
    (syntax-rules ()
      (_ 8)))

(+ 3 eight) ⇒ 11
(eight) ⇒ ERROR
(set! eight 9) ⇒ ERROR

4.9.4 Macro Primitives ¶

Function: procedure->syntax proc ¶

Returns a macro which, when a symbol defined to this value appears as the first symbol in an expression, returns the result of applying proc to the expression and the environment.

Function: procedure->macro proc ¶

Function: procedure->memoizing-macro proc ¶

Function: procedure->identifier-macro ¶

Returns a macro which, when a symbol defined to this value appears as the first symbol in an expression, evaluates the result of applying proc to the expression and the environment. The value returned from proc which has been passed to PROCEDURE->MEMOIZING-MACRO replaces the form passed to proc. For example:

(defsyntax trace
  (procedure->macro
   (lambda (x env) `(set! ,(cadr x) (tracef ,(cadr x) ',(cadr x))))))

(trace foo) ≡ (set! foo (tracef foo 'foo)).

PROCEDURE->IDENTIFIER-MACRO is similar to PROCEDURE->MEMOIZING-MACRO except that proc is also called in case the symbol bound to the macro appears in an expression but not as the first symbol, that is, when it looks like a variable reference. In that case, the form passed to proc is a single identifier.

Special Form: defsyntax name expr ¶

Defines name as a macro keyword bound to the result of evaluating expr, which should be a macro. Using define for this purpose may not result in name being interpreted as a macro keyword.

4.9.5 Environment Frames ¶

An environment is a list of frames representing lexical bindings. Only the names and scope of the bindings are included in environments passed to macro expanders – run-time values are not included.

There are several types of environment frames:

((lambda (variable1 …) …) value1 …)

(let ((variable1 value1) (variable2 value2) …) …)

(letrec ((variable1 value1) …) …)

result in a single enviroment frame:

(variable1 variable2 ...)

(let ((variable1 value1)) …)

(let* ((variable1 value1) …) …)

result in an environment frame for each variable:

variable1 variable2 ...

(let-syntax ((key1 macro1) (key2 macro2)) …)

(letrec-syntax ((key1 value1) (key2 value2)) …)

Lexically bound macros result in environment frames consisting of a marker and an alist of keywords and macro objects:

(<env-syntax-marker> (key1 . value1) (key2 . value2))

Currently <env-syntax-marker> is the integer 6.

line numbers

Line numbers (see Line Numbers) may be included in the environment as frame entries to indicate the line number on which a function is defined. They are ignored for variable lookup.

#<line 8> 

miscellaneous

Debugging information is stored in environments in a plist format: Any exact integer stored as an environment frame may be followed by any value. The two frame entries are ignored when doing variable lookup. Load file names, procedure names, and closure documentation strings are stored in this format.

<env-filename-marker> "foo.scm" <env-procedure-name-marker> foo ...

Currently <env-filename-marker> is the integer 1 and <env-procedure-name-marker> the integer 2.

Special Form: @apply procedure argument-list ¶

Returns the result of applying procedure to argument-list. @apply differs from apply when the identifiers bound by the closure being applied are set!; setting affects argument-list.

(define lst (list 'a 'b 'c))
(@apply (lambda (v1 v2 v3) (set! v1 (cons v2 v3))) lst)
lst           ⇒ ((b . c) b c)

Thus a mutable environment can be treated as both a list and local bindings.

4.9.6 Syntactic Hooks for Hygienic Macros ¶

SCM provides a synthetic identifier type for efficient implementation of hygienic macros (for example, syntax-rules see Macros in Revised(5) Scheme) A synthetic identifier may be inserted in Scheme code by a macro expander in any context where a symbol would normally be used. Collectively, symbols and synthetic identifiers are identifiers.

Function: identifier? obj ¶

Returns #t if obj is a symbol or a synthetic identifier, and #f otherwise.

If it is necessary to distinguish between symbols and synthetic identifiers, use the predicate symbol?.

A synthetic identifier includes two data: a parent, which is an identifier, and an environment, which is either #f or a lexical environment which has been passed to a macro expander (a procedure passed as an argument to procedure->macro, procedure->memoizing-macro, or procedure->syntax).

Function: renamed-identifier parent env ¶

Returns a synthetic identifier. parent must be an identifier, and env must either be #f or a lexical environment passed to a macro expander. renamed-identifier returns a distinct object for each call, even if passed identical arguments.

There is no direct way to access all of the data internal to a synthetic identifier, those data are used during variable lookup. If a synthetic identifier is inserted as quoted data then during macro expansion it will be repeatedly replaced by its parent, until a symbol is obtained.

Function: identifier->symbol id ¶

Returns the symbol obtained by recursively extracting the parent of id, which must be an identifier.

4.9.7 Use of Synthetic Identifiers ¶

renamed-identifier may be used as a replacement for gentemp:

(define gentemp
  (let ((name (string->symbol "An unlikely variable")))
    (lambda ()
      (renamed-identifier name #f))))

If an identifier returned by this version of gentemp is inserted in a binding position as the name of a variable then it is guaranteed that no other identifier (except one produced by passing the first to renamed-identifier) may denote that variable. If an identifier returned by gentemp is inserted free, then it will denote the top-level value bound to its parent, the symbol named “An unlikely variable”. This behavior, of course, is meant to be put to good use:

(define top-level-foo
  (procedure->memoizing-macro
   (lambda (exp env)
     (renamed-identifier 'foo #f))))

Defines a macro which may always be used to refer to the top-level binding of foo.

(define foo 'top-level)
(let ((foo 'local))
  (top-level-foo))  ⇒ top-level

In other words, we can avoid capturing foo.

If a lexical environment is passed as the second argument to renamed-identifier then if the identifier is inserted free its parent will be looked up in that environment, rather than in the top-level environment. The use of such an identifier must be restricted to the lexical scope of its environment.

There is another restriction imposed for implementation convenience: Macros passing their lexical environments to renamed-identifier may be lexically bound only by the special forms let-syntax or letrec-syntax. No error is signaled if this restriction is not met, but synthetic identifier lookup will not work properly.

In order to maintain referential transparency it is necessary to determine whether two identifiers have the same denotation. With synthetic identifiers it is not necessary that two identifiers be eq? in order to denote the same binding.

Function: identifier-equal? id1 id2 env ¶

Returns #t if identifiers id1 and id2 denote the same binding in lexical environment env, and #f otherwise. env must either be a lexical environment passed to a macro transformer during macro expansion or the empty list.

For example,

(define top-level-foo?
  (procedure->memoizing-macro
   (let ((foo-name (renamed-identifier 'foo #f)))
     (lambda (exp env)
       (identifier-equal? (cadr exp) foo-name env)))))

(top-level-foo? foo)  ⇒ #t

(let ((foo 'local))
  (top-level-foo? foo))  ⇒ #f

Function: @macroexpand1 expr env ¶

If the car of expr denotes a macro in env, then if that macro is a primitive, expr will be returned, if the macro was defined in Scheme, then a macro expansion will be returned. If the car of expr does not denote a macro, the #f is returned.

Function: extended-environment names values env ¶

Returns a new environment object, equivalent to env, which must either be an environment object or null, extended by one frame. names must be an identifier, or an improper list of identifiers, usable as a formals list in a lambda expression. values must be a list of objects long enough to provide a binding for each of the identifiers in names. If names is an identifier or an improper list then vals may be, respectively, any object or an improper list of objects.

Special Form: syntax-quote obj ¶

Synthetic identifiers are converted to their parent symbols by quote and quasiquote so that literal data in macro definitions will be properly transcribed. syntax-quote behaves like quote, but preserves synthetic identifier intact.

Special Form: the-macro mac ¶

the-macro is the simplest of all possible macro transformers: mac may be a syntactic keyword (macro name) or an expression evaluating to a macro, otherwise an error is signaled. mac is evaluated and returned once only, after which the same memoizied value is returned.

the-macro may be used to protect local copies of macros against redefinition, for example:

(@let-syntax ((let (the-macro let)))
   ;; code that will continue to work even if LET is redefined.
        ...)

Special Form: renaming-transformer proc ¶

A low-level “explicit renaming” macro facility very similar to that proposed by W. Clinger [Exrename] is supported. Syntax may be defined in define-syntax, let-syntax, and letrec-syntax using renaming-transformer instead of syntax-rules. proc should evaluate to a procedure accepting three arguments: expr, rename, and compare. expr is a representation of Scheme code to be expanded, as list structure. rename is a procedure accepting an identifier and returning an identifier renamed in the definition environment of the new syntax. compare accepts two identifiers and returns true if and only if both denote the same binding in the usage environment of the new syntax.