Petar Kapriš
2ca5e73a27
Notes: The exercise 2.37 on Hexlet's site has an error, noted in the comments. Also, their page for exercise 2.38 should probably have 0 tests. And finally, I did not calculate the exact number in the final exercise 2.43, but I included a relevant discussion.
22 lines
655 B
Scheme
22 lines
655 B
Scheme
#lang sicp
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(define (fold-right op initial sequence)
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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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(define (fold-left op initial sequence)
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(define (iter result rest)
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(if (null? rest)
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result
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(iter (op result (car rest))
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(cdr rest))))
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(iter initial sequence))
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; (fold-right / 1 (list 1 2 3)) -> (1/(2/(3/1))) = 3/2
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; (fold-left / 1 (list 1 2 3)) -> (((1/1)/2)/3) = 1/6
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; (fold-right list nil (list 1 2 3)) -> (1 (2 (3 ())))
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; (fold-left list nil (list 1 2 3)) -> (((() 1) 2) 3)
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; in order to produce the same results, the operation
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; must be associative.
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