/
stream.rkt
163 lines (145 loc) · 4.91 KB
/
stream.rkt
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
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
#lang racket/base
(require "private/for.rkt"
"private/sequence.rkt"
(only-in "private/stream-cons.rkt"
stream-cons))
(provide empty-stream
stream-cons
stream?
stream-empty?
stream-first
stream-rest
prop:stream
in-stream
stream
stream->list
stream-length
stream-ref
stream-tail
stream-append
stream-map
stream-andmap
stream-ormap
stream-for-each
stream-fold
stream-filter
stream-add-between
stream-count)
(define-syntax stream
(syntax-rules ()
((_)
empty-stream)
((_ hd tl ...)
(stream-cons hd (stream tl ...)))))
(define (stream->list s)
(for/list ([v (in-stream s)]) v))
(define (stream-length s)
(unless (stream? s) (raise-type-error 'stream-length "stream" s))
(let loop ([s s] [len 0])
(if (stream-empty? s)
len
(loop (stream-rest s) (add1 len)))))
(define (stream-ref st i)
(unless (stream? st) (raise-type-error 'stream-ref "stream" st))
(unless (exact-nonnegative-integer? i)
(raise-type-error 'stream-ref "nonnegative exact integer" i))
(let loop ([n i] [s st])
(cond
[(stream-empty? s)
(raise-mismatch-error 'stream-ref
(format "sequence ended before element ~e: "
(add1 i))
st)]
[(zero? n)
(stream-first s)]
[else
(loop (sub1 n) (stream-rest s))])))
(define (stream-tail st i)
(unless (stream? st) (raise-type-error 'stream-tail "stream" st))
(unless (exact-nonnegative-integer? i)
(raise-type-error 'stream-tail "nonnegative exact integer" i))
(let loop ([n i] [s st])
(cond
[(zero? n) s]
[(stream-empty? s)
(raise-mismatch-error
'stream-tail
(format "sequence ended before ~e element~a: "
i
(if (= i 1) "" "s"))
st)]
[else
(loop (sub1 n) (stream-rest s))])))
(define (stream-append . l)
(for ([s (in-list l)])
(unless (stream? s) (raise-type-error 'stream-append "stream" s)))
(streams-append l))
(define (streams-append l)
(cond
[(null? l) empty-stream]
[(stream-empty? (car l)) (streams-append (cdr l))]
[else
(make-do-stream (lambda () #f)
(lambda () (stream-first (car l)))
(lambda () (streams-append (cons (stream-rest (car l)) (cdr l)))))]))
(define (stream-map f s)
(unless (procedure? f) (raise-type-error 'stream-map "procedure" f))
(unless (stream? s) (raise-type-error 'stream-map "stream" s))
(let loop ([s s])
(cond
[(stream-empty? s) empty-stream]
[else (stream-cons (call-with-values (lambda () (stream-first s)) f)
(loop (stream-rest s)))])))
(define (stream-andmap f s)
(unless (procedure? f) (raise-type-error 'stream-andmap "procedure" f))
(unless (stream? s) (raise-type-error 'stream-andmap "stream" s))
(sequence-andmap f s))
(define (stream-ormap f s)
(unless (procedure? f) (raise-type-error 'stream-ormap "procedure" f))
(unless (stream? s) (raise-type-error 'stream-ormap "stream" s))
(sequence-ormap f s))
(define (stream-for-each f s)
(unless (procedure? f) (raise-type-error 'stream-for-each "procedure" f))
(unless (stream? s) (raise-type-error 'stream-for-each "stream" s))
(sequence-for-each f s))
(define (stream-fold f i s)
(unless (procedure? f) (raise-type-error 'stream-fold "procedure" f))
(unless (stream? s) (raise-type-error 'stream-fold "stream" s))
(sequence-fold f i s))
(define (stream-count f s)
(unless (procedure? f) (raise-type-error 'stream-count "procedure" f))
(unless (stream? s) (raise-type-error 'stream-count "stream" s))
(sequence-count f s))
(define (stream-filter f s)
(unless (procedure? f) (raise-type-error 'stream-filter "procedure" f))
(unless (stream? s) (raise-type-error 'stream-filter "stream" s))
(cond
[(stream-empty? s) empty-stream]
[else
(let ([done? #f]
[empty? #f]
[fst #f]
[rst #f])
(define (force!)
(unless done?
(let loop ([s s])
(cond
[(stream-empty? s)
(set! done? #t)
(set! empty? #t)]
[(f (stream-first s))
(set! fst (stream-first s))
(set! rst (stream-filter f (stream-rest s)))]
[else (loop (stream-rest s))]))
(set! done? #t)))
(make-do-stream (lambda () (force!) empty?)
(lambda () (force!) fst)
(lambda () (force!) rst)))]))
(define (stream-add-between s e)
(unless (stream? s)
(raise-type-error 'stream-add-between "stream" s))
(let loop ([s s])
(cond
[(stream-empty? s) empty-stream]
[else (stream-cons (stream-first s)
(stream-cons e (loop (stream-rest s))))])))