133 lines
3.1 KiB
Scheme
133 lines
3.1 KiB
Scheme
(define (assert a b)
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(cond ((equal? a b) (display "[ok]"))
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(else
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(display "[error] ")
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(display a)
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(display " != ")
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(display b)))
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(newline))
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; I have this here to avoid name-conflicts with the amb implementation in
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; amb.scm.
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(define (my-assert a b)
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(cond ((equal? a b) (display "[ok]"))
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(else
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(display "[error] ")
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(display a)
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(display " != ")
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(display b)))
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(newline))
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(define (gcd a b)
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(if (= b 0) (abs a) (gcd b (remainder a b))))
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(define (average a b) (/ (+ a b) 2.0))
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(define (id n) n)
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(define identity id)
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(define (inc n) (+ n 1))
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(define nil '())
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(define (divides? a b) (= (remainder b a) 0))
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(define (cube n) (* n n n))
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(define (even? n) (= (remainder n 2) 0))
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(define (odd? n) (= (remainder n 2) 1))
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; copied prime? from 1.21
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(define (find-divisor n test-divisor)
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(cond ((> (square test-divisor) n) n)
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((divides? test-divisor n) test-divisor)
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(else (find-divisor n (+ test-divisor 1)))))
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(define (smallest-divisor n)
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(find-divisor n 2))
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(define (prime? n) (if (= n 1) #f (= n (smallest-divisor n))))
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; https://mitpress.mit.edu/sites/default/files/sicp/full-text/book/book-Z-H-15.html
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(define (enumerate-interval low high)
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(if (> low high)
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nil
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(cons low (enumerate-interval (+ low 1) high))))
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; Returns #t if there is no #f in xs, otherwise returns #f.
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(define (all? xs)
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(cond ((null? xs) #t)
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((eq? (car xs) #f) #f)
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(else (all? (cdr xs)))))
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(define (all-eq? xs)
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(cond ((null? xs) #t)
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((null? (cdr xs)) #t)
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((eq? (car xs) (cadr xs)) (all-eq? (cdr xs)))
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(else #f)))
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(define (fold-right op initial sequence) ; same as accumulate
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(if (null? sequence)
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initial
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(op (car sequence)
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(fold-right op initial (cdr sequence)))))
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; From exercise 3.5
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(define (random-in-range low high)
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(let ((range (- high low)))
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(+ low (random range))))
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(define (contains x xs)
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(cond
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((null? xs) #f)
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((eq? x (car xs)) #t)
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(else (contains x (cdr xs)))))
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(define (display-line x)
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(display x)
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(newline))
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(define (take n xs)
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(if (= n 0)
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'()
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(cons (stream-car xs)
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(take (- n 1) (stream-cdr xs)))))
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(define (drop n xs)
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(if (= n 0)
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xs
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(drop (- n 1) (stream-cdr xs))))
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(define (find item stream)
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(define (iter n stream)
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(if (equal? (stream-car stream) item)
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n
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(iter (+ n 1) (stream-cdr stream))))
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(iter 0 stream))
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(define (display-stream s)
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(stream-for-each display-line s))
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(define (show x)
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(display-line x)
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x)
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(define (stream-ref s n)
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(if (= n 0)
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(stream-car s)
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(stream-ref (stream-cdr s) (- n 1))))
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(define (partial-sums xs)
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(cons-stream (stream-car xs)
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(add-streams (partial-sums xs)
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(stream-cdr xs))))
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(define (scale-stream stream factor)
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(stream-map (lambda (x) (* x factor)) stream))
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(define (add-streams s1 s2)
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(stream-map + s1 s2))
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(define (list->stream xs)
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(if (null? xs)
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'()
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(cons-stream (car xs) (list->stream (cdr xs)))))
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(define ones (cons-stream 1 ones))
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(define integers (cons-stream 1 (add-streams ones integers)))
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'util-loaded
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