48 lines
1.5 KiB
Scheme
48 lines
1.5 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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(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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; Put and get functions. We could have implemented this via a list of
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; three-tuples, but I don't know how to create global variables yet so we just
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; use this code from SO. Doesn't look too complicated.
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; https://stackoverflow.com/questions/5499005/how-do-i-get-the-functions-put-and-get-in-sicp-scheme-exercise-2-78-and-on
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(define *op-table* (make-hash-table))
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(define (put op type proc)
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(hash-table/put! *op-table* (list op type) proc))
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(define (get op type)
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(hash-table/get *op-table* (list op type) #f))
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