#| -*-Scheme-*-

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    2017, 2018, 2019, 2020, 2021, 2022 Massachusetts Institute of
    Technology

This file is part of MIT/GNU Scheme.

MIT/GNU Scheme is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or (at
your option) any later version.

MIT/GNU Scheme is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
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General Public License for more details.

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|#

;;;; Support for enumerations

(declare (usual-integrations))

;;;; Enumerations

(define-structure (enumeration
		   (conc-name enumeration/)
		   (constructor %make-enumeration))
  (enumerands false read-only true))

(define-structure (enumerand
		   (conc-name enumerand/)
		   (print-procedure
		    (standard-print-method "LIAR:enumerand"
		      (lambda (enumerand)
			(list (enumerand/name enumerand))))))
  (enumeration false read-only true)
  (name false read-only true)
  (index false read-only true))

(define (make-enumeration names)
  (let ((enumerands (make-vector (length names))))
    (let ((enumeration (%make-enumeration enumerands)))
      (let loop ((names names) (index 0))
	(if (not (null? names))
	    (begin
	      (vector-set! enumerands
			   index
			   (make-enumerand enumeration (car names) index))
	      (loop (cdr names) (1+ index)))))
      enumeration)))

(define-integrable (enumeration/cardinality enumeration)
  (vector-length (enumeration/enumerands enumeration)))

(define-integrable (enumeration/index->enumerand enumeration index)
  (vector-ref (enumeration/enumerands enumeration) index))

(define-integrable (enumeration/index->name enumeration index)
  (enumerand/name (enumeration/index->enumerand enumeration index)))

(define (enumeration/name->enumerand enumeration name)
  (let ((end (enumeration/cardinality enumeration)))
    (let loop ((index 0))
      (if (< index end)
	  (let ((enumerand (enumeration/index->enumerand enumeration index)))
	    (if (eqv? (enumerand/name enumerand) name)
		enumerand
		(loop (1+ index))))
	  (error "Unknown enumeration name" name)))))

(define-integrable (enumeration/name->index enumeration name)
  (enumerand/index (enumeration/name->enumerand enumeration name)))

;;;; Method Tables

(define-structure (method-table (constructor %make-method-table))
  (enumeration false read-only true)
  (vector false read-only true))

(define (make-method-table enumeration default-method . method-alist)
  (let ((table
	 (%make-method-table enumeration
			     (make-vector (enumeration/cardinality enumeration)
					  default-method))))
    (for-each (lambda (entry)
		(define-method-table-entry table (car entry) (cdr entry)))
	      method-alist)
    table))

(define (define-method-table-entry name method-table method)
  (vector-set! (method-table-vector method-table)
	       (enumeration/name->index (method-table-enumeration method-table)
					name)
	       method)
  name)

(define (define-method-table-entries names method-table method)
  (for-each (lambda (name)
	      (define-method-table-entry name method-table method))
	    names)
  names)

(define-integrable (method-table-lookup method-table index)
  (vector-ref (method-table-vector method-table) index))