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8cdfb9aa JB |
1 | ;;;; streams.scm --- general lazy streams |
2 | ;;;; -*- Scheme -*- | |
3 | ||
cd5fea8d | 4 | ;;;; Copyright (C) 1999, 2001, 2004, 2006 Free Software Foundation, Inc. |
8cdfb9aa | 5 | ;;;; |
73be1d9e MV |
6 | ;;;; This library is free software; you can redistribute it and/or |
7 | ;;;; modify it under the terms of the GNU Lesser General Public | |
8 | ;;;; License as published by the Free Software Foundation; either | |
9 | ;;;; version 2.1 of the License, or (at your option) any later version. | |
8cdfb9aa | 10 | ;;;; |
73be1d9e | 11 | ;;;; This library is distributed in the hope that it will be useful, |
8cdfb9aa | 12 | ;;;; but WITHOUT ANY WARRANTY; without even the implied warranty of |
73be1d9e MV |
13 | ;;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
14 | ;;;; Lesser General Public License for more details. | |
8cdfb9aa | 15 | ;;;; |
73be1d9e MV |
16 | ;;;; You should have received a copy of the GNU Lesser General Public |
17 | ;;;; License along with this library; if not, write to the Free Software | |
92205699 | 18 | ;;;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA |
8cdfb9aa JB |
19 | |
20 | ;; the basic stream operations are inspired by | |
21 | ;; (i.e. ripped off) Scheme48's `stream' package, | |
22 | ;; modulo stream-empty? -> stream-null? renaming. | |
23 | ||
1a179b03 MD |
24 | (define-module (ice-9 streams) |
25 | :export (make-stream | |
26 | stream-car stream-cdr stream-null? | |
27 | list->stream vector->stream port->stream | |
28 | stream->list stream->reversed-list | |
29 | stream->list&length stream->reversed-list&length | |
30 | stream->vector | |
31 | stream-fold stream-for-each stream-map)) | |
8cdfb9aa JB |
32 | |
33 | ;; Use: | |
34 | ;; | |
35 | ;; (make-stream producer initial-state) | |
36 | ;; - PRODUCER is a function of one argument, the current state. | |
37 | ;; it should return either a pair or an atom (i.e. anything that | |
38 | ;; is not a pair). if PRODUCER returns a pair, then the car of the pair | |
39 | ;; is the stream's head value, and the cdr is the state to be fed | |
40 | ;; to PRODUCER later. if PRODUCER returns an atom, then the stream is | |
41 | ;; considered depleted. | |
42 | ;; | |
43 | ;; (stream-car stream) | |
44 | ;; (stream-cdr stream) | |
45 | ;; (stream-null? stream) | |
46 | ;; - yes. | |
47 | ;; | |
48 | ;; (list->stream list) | |
49 | ;; (vector->stream vector) | |
50 | ;; - make a stream with the same contents as LIST/VECTOR. | |
51 | ;; | |
52 | ;; (port->stream port read) | |
53 | ;; - makes a stream of values which are obtained by READing from PORT. | |
54 | ;; | |
55 | ;; (stream->list stream) | |
56 | ;; - returns a list with the same contents as STREAM. | |
57 | ;; | |
58 | ;; (stream->reversed-list stream) | |
59 | ;; - as above, except the contents are in reversed order. | |
60 | ;; | |
61 | ;; (stream->list&length stream) | |
62 | ;; (stream->reversed-list&length stream) | |
63 | ;; - multiple-valued versions of the above two, the second value is the | |
64 | ;; length of the resulting list (so you get it for free). | |
65 | ;; | |
66 | ;; (stream->vector stream) | |
67 | ;; - yes. | |
68 | ;; | |
69 | ;; (stream-fold proc init stream0 ...) | |
70 | ;; - PROC must take (+ 1 <number-of-stream-arguments>) arguments, like this: | |
71 | ;; (PROC car0 ... init). *NOTE*: the INIT argument is last, not first. | |
72 | ;; I don't have any preference either way, but it's consistent with | |
73 | ;; `fold[lr]' procedures from SRFI-1. PROC is applied to successive | |
74 | ;; elements of the given STREAM(s) and to the value of the previous | |
75 | ;; invocation (INIT on the first invocation). the last result from PROC | |
76 | ;; is returned. | |
77 | ;; | |
78 | ;; (stream-for-each proc stream0 ...) | |
79 | ;; - like `for-each' we all know and love. | |
80 | ;; | |
81 | ;; (stream-map proc stream0 ...) | |
82 | ;; - like `map', except returns a stream of results, and not a list. | |
83 | ||
84 | ;; Code: | |
85 | ||
86 | (define (make-stream m state) | |
87 | (delay | |
88 | (let ((o (m state))) | |
89 | (if (pair? o) | |
90 | (cons (car o) | |
91 | (make-stream m (cdr o))) | |
92 | '())))) | |
93 | ||
94 | (define (stream-car stream) | |
ed11b876 | 95 | "Returns the first element in STREAM. This is equivalent to `car'." |
8cdfb9aa JB |
96 | (car (force stream))) |
97 | ||
98 | (define (stream-cdr stream) | |
ed11b876 | 99 | "Returns the first tail of STREAM. Equivalent to `(force (cdr STREAM))'." |
8cdfb9aa JB |
100 | (cdr (force stream))) |
101 | ||
102 | (define (stream-null? stream) | |
ed11b876 GB |
103 | "Returns `#t' if STREAM is the end-of-stream marker; otherwise |
104 | returns `#f'. This is equivalent to `null?', but should be used | |
105 | whenever testing for the end of a stream." | |
8cdfb9aa JB |
106 | (null? (force stream))) |
107 | ||
108 | (define (list->stream l) | |
ed11b876 GB |
109 | "Returns a newly allocated stream whose elements are the elements of |
110 | LIST. Equivalent to `(apply stream LIST)'." | |
8cdfb9aa JB |
111 | (make-stream |
112 | (lambda (l) l) | |
113 | l)) | |
114 | ||
115 | (define (vector->stream v) | |
116 | (make-stream | |
117 | (let ((len (vector-length v))) | |
118 | (lambda (i) | |
119 | (or (= i len) | |
120 | (cons (vector-ref v i) (+ 1 i))))) | |
121 | 0)) | |
122 | ||
123 | (define (stream->reversed-list&length stream) | |
124 | (let loop ((s stream) (acc '()) (len 0)) | |
125 | (if (stream-null? s) | |
126 | (values acc len) | |
127 | (loop (stream-cdr s) (cons (stream-car s) acc) (+ 1 len))))) | |
128 | ||
129 | (define (stream->reversed-list stream) | |
130 | (call-with-values | |
131 | (lambda () (stream->reversed-list&length stream)) | |
132 | (lambda (l len) l))) | |
133 | ||
134 | (define (stream->list&length stream) | |
135 | (call-with-values | |
136 | (lambda () (stream->reversed-list&length stream)) | |
137 | (lambda (l len) (values (reverse! l) len)))) | |
138 | ||
139 | (define (stream->list stream) | |
ed11b876 GB |
140 | "Returns a newly allocated list whose elements are the elements of STREAM. |
141 | If STREAM has infinite length this procedure will not terminate." | |
8cdfb9aa JB |
142 | (reverse! (stream->reversed-list stream))) |
143 | ||
144 | (define (stream->vector stream) | |
145 | (call-with-values | |
146 | (lambda () (stream->reversed-list&length stream)) | |
147 | (lambda (l len) | |
148 | (let ((v (make-vector len))) | |
149 | (let loop ((i 0) (l l)) | |
150 | (if (not (null? l)) | |
151 | (begin | |
152 | (vector-set! v (- len i 1) (car l)) | |
153 | (loop (+ 1 i) (cdr l))))) | |
154 | v)))) | |
155 | ||
156 | (define (stream-fold f init stream . rest) | |
157 | (if (null? rest) ;fast path | |
b87e3d4d ML |
158 | (stream-fold-one f init stream) |
159 | (stream-fold-many f init (cons stream rest)))) | |
160 | ||
161 | (define (stream-fold-one f r stream) | |
162 | (if (stream-null? stream) | |
163 | r | |
164 | (stream-fold-one f (f (stream-car stream) r) (stream-cdr stream)))) | |
165 | ||
166 | (define (stream-fold-many f r streams) | |
167 | (if (or-map stream-null? streams) | |
168 | r | |
169 | (stream-fold-many f | |
170 | (apply f (let recur ((cars | |
171 | (map stream-car streams))) | |
172 | (if (null? cars) | |
173 | (list r) | |
174 | (cons (car cars) | |
175 | (recur (cdr cars)))))) | |
176 | (map stream-cdr streams)))) | |
8cdfb9aa JB |
177 | |
178 | (define (stream-for-each f stream . rest) | |
b87e3d4d ML |
179 | (if (null? rest) ;fast path |
180 | (stream-for-each-one f stream) | |
181 | (stream-for-each-many f (cons stream rest)))) | |
182 | ||
183 | (define (stream-for-each-one f stream) | |
184 | (if (not (stream-null? stream)) | |
185 | (begin | |
186 | (f (stream-car stream)) | |
187 | (stream-for-each-one f (stream-cdr stream))))) | |
188 | ||
fc7a9e81 | 189 | (define (stream-for-each-many f streams) |
b87e3d4d ML |
190 | (if (not (or-map stream-null? streams)) |
191 | (begin | |
192 | (apply f (map stream-car streams)) | |
f749e803 | 193 | (stream-for-each-many f (map stream-cdr streams))))) |
8cdfb9aa JB |
194 | |
195 | (define (stream-map f stream . rest) | |
ed11b876 GB |
196 | "Returns a newly allocated stream, each element being the result of |
197 | invoking F with the corresponding elements of the STREAMs | |
198 | as its arguments." | |
8cdfb9aa JB |
199 | (if (null? rest) ;fast path |
200 | (make-stream (lambda (s) | |
201 | (or (stream-null? s) | |
202 | (cons (f (stream-car s)) (stream-cdr s)))) | |
203 | stream) | |
204 | (make-stream (lambda (streams) | |
205 | (or (or-map stream-null? streams) | |
206 | (cons (apply f (map stream-car streams)) | |
207 | (map stream-cdr streams)))) | |
208 | (cons stream rest)))) | |
209 | ||
210 | (define (port->stream port read) | |
211 | (make-stream (lambda (p) | |
212 | (let ((o (read p))) | |
213 | (or (eof-object? o) | |
214 | (cons o p)))) | |
215 | port)) | |
216 | ||
217 | ;;; streams.scm ends here |