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28 lines
797 B
28 lines
797 B
2 years ago
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Exercise 2.38: The accumulate procedure
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is also known as fold-right, because it combines the first element of
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the sequence with the result of combining all the elements to the right. There
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is also a fold-left, which is similar to fold-right, except that
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it combines elements working in the opposite direction:
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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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What are the values of
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(fold-right / 1 (list 1 2 3))
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(fold-left / 1 (list 1 2 3))
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(fold-right list nil (list 1 2 3))
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(fold-left list nil (list 1 2 3))
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Give a property that op should satisfy to guarantee that
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fold-right and fold-left will produce the same values for any
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sequence.
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