blob: eb3a13fcaa8bf0dc197859552c2f42867055cb12 (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
|
;;; 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)))))
|