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- ;;; installed-scm-file
-
- ;;;; Copyright (C) 1996, 2001, 2006 Free Software Foundation, Inc.
- ;;;;
- ;;;; This library 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 2.1 of the License, or (at your option) any later version.
- ;;;;
- ;;;; This library 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 library; if not, write to the Free Software
- ;;;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
- ;;;;
-
-
- (define-module (ice-9 poe)
- :use-module (ice-9 hcons)
- :export (pure-funcq perfect-funcq))
-
-
-
-
- ;;; {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))
-
- ;; return true if lists X and Y are the same length and each element is `eq?'
- (define (eq?-list x y)
- (if (null? x)
- (null? y)
- (and (not (null? y))
- (eq? (car x) (car y))
- (eq?-list (cdr x) (cdr y)))))
-
- (define (funcq-assoc arg-list alist)
- (if (null? alist)
- #f
- (if (eq?-list arg-list (caar alist))
- (car alist)
- (funcq-assoc arg-list (cdr alist)))))
-
-
-
- (define (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 (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)))))
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