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22 lines
605 B
Racket
22 lines
605 B
Racket
#lang racket/base
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(require racket/list racket/bool)
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(provide (all-defined-out))
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(module+ test (require rackunit))
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(define (count_if pred xs)
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;; Count the number of elements of seq for which the predicate is true.
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(length (filter-not false? (map pred xs))))
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(module+ test
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(check-equal? (count_if procedure? (list 42 null max min)) 2))
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(define (find_if pred xs)
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;; If there is an element of seq that satisfies predicate; return it.
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(or (findf pred xs) null))
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(module+ test
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(check-equal? (find_if procedure? (list 3 min max)) min)
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(check-equal? (find_if procedure? (list 1 2 3)) null))
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