77 lines
1.7 KiB
Scheme
77 lines
1.7 KiB
Scheme
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#lang sicp
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(define (gcd a b)
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(if (= b 0)
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a
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(gcd b (remainder a b))))
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(define (add-rat x y)
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(make-rat (+ (* (numer x) (denom y))
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(* (numer y) (denom x)))
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(* (denom x) (denom y))))
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(define (sub-rat x y)
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(make-rat (- (* (numer x) (denom y))
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(* (numer y) (denom x)))
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(* (denom x) (denom y))))
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(define (mul-rat x y)
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(make-rat (* (numer x) (numer y))
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(* (denom x) (denom y))))
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(define (div-rat x y)
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(make-rat (* (numer x) (denom y))
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(* (denom x) (numer y))))
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(define (equal-rat? x y)
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(= (* (numer x) (denom y))
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(* (numer y) (denom x))))
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(define (make-rat n d)
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(let ((g (gcd n d)))
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(cons (/ n g)
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(/ d g))))
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(define (numer x) (car x))
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(define (denom x) (cdr x))
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(define (print-rat x)
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(newline)
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(display (numer x))
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(display "/")
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(display (denom x)))
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(define one-half (make-rat 1 2))
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(define one-third (make-rat 1 3))
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(define one-through-four (list 1 2 3 4))
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(define (list-ref items n)
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(if (= n 0)
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(car items)
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(list-ref (cdr items)
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(- n 1))))
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;(define (length items)
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; (if (null? items)
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; 0
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; (+ 1 (length (cdr items)))))
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(define (length items)
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(define (length-iter a count)
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(if (null? a)
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count
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(length-iter (cdr a)
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(+ 1 count))))
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(length-iter items 0))
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(define (append list1 list2)
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(if (null? list1)
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list2
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(cons (car list1)
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(append (cdr list1)
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list2))))
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(define (scale-list items factor)
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(if (null? items)
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nil
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(cons (* (car items) factor)
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(scale-list (cdr items)
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factor))))
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