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-;;; installed-scm-file
-
-;;;; Copyright (C) 1996 Free Software Foundation, Inc.
-;;;;
-;;;; This program 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, 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 General Public License for more details.
-;;;;
-;;;; You should have received a copy of the GNU General Public License
-;;;; along with this software; see the file COPYING. If not, write to
-;;;; the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
-;;;;
-
-
-(define-module #/ice-9/poe
- :use-module #/ice-9/hcons)
-
-
-
-
-;;; {Pure Functions}
-;;;
-;;; A pure function (of some sort) is characterized by two equality
-;;; relations: one on argument lists and one on return values.
-;;; A pure function is one that when applied to equal arguments lists
-;;; yields equal results.
-;;;
-;;; If the equality relationship on return values can be eq?, it may make
-;;; sense to cache values returned by the function. Choosing the right
-;;; equality relation on arguments is tricky.
-;;;
-
-
-;;; {pure-funcq}
-;;;
-;;; The simplest case of pure functions are those in which results
-;;; are only certainly eq? if all of the arguments are. These functions
-;;; are called "pure-funcq", for obvious reasons.
-;;;
-
-
-(define funcq-memo (make-weak-key-hash-table 523)) ; !!! randomly selected values
-(define funcq-buffer (make-gc-buffer 256))
-
-(define (funcq-hash arg-list n)
- (let ((it (let loop ((x 0)
- (arg-list arg-list))
- (if (null? arg-list)
- (modulo x n)
- (loop (logior x (hashq (car arg-list) 4194303))
- (cdr arg-list))))))
- it))
-
-(define (funcq-assoc arg-list alist)
- (let ((it (and alist
- (let and-map ((key arg-list)
- (entry (caar alist)))
- (or (and (and (not key) (not entry))
- (car alist))
- (and key entry
- (eq? (car key) (car entry))
- (and-map (cdr key) (cdr entry))))))))
- it))
-
-
-
-(define-public (pure-funcq base-func)
- (lambda args
- (let ((cached (hashx-get-handle funcq-hash funcq-assoc funcq-memo (cons base-func args))))
- (if cached
- (begin
- (funcq-buffer (car cached))
- (cdr cached))
-
- (let ((val (apply base-func args))
- (key (cons base-func args)))
- (funcq-buffer key)
- (hashx-set! funcq-hash funcq-assoc funcq-memo key val)
- val)))))
-
-
-
-;;; {Perfect funq}
-;;;
-;;; A pure funq may sometimes forget its past but a perfect
-;;; funcq never does.
-;;;
-
-(define-public (perfect-funcq size base-func)
- (define funcq-memo (make-hash-table size))
-
- (lambda args
- (let ((cached (hashx-get-handle funcq-hash funcq-assoc funcq-memo (cons base-func args))))
- (if cached
- (begin
- (funcq-buffer (car cached))
- (cdr cached))
-
- (let ((val (apply base-func args))
- (key (cons base-func args)))
- (funcq-buffer key)
- (hashx-set! funcq-hash funcq-assoc funcq-memo key val)
- val)))))
-
-
-
-
-
-
-
-