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35 lines
1 KiB
Scheme
35 lines
1 KiB
Scheme
;; search.scm -- list searching and splitting
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;; Copyright (c) 2009-2011 Alex Shinn. All rights reserved.
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;; BSD-style license: http://synthcode.com/license.txt
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(define (take-while pred ls)
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(let lp ((ls ls) (res '()))
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(if (and (pair? ls) (pred (car ls)))
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(lp (cdr ls) (cons (car ls) res))
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(reverse! res))))
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(define take-while! take-while)
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(define (drop-while pred ls)
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(or (find-tail (lambda (x) (not (pred x))) ls) '()))
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(define (span pred ls)
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(let lp ((ls ls) (res '()))
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(if (and (pair? ls) (pred (car ls)))
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(lp (cdr ls) (cons (car ls) res))
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(values (reverse! res) ls))))
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(define span! span)
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(define (break pred ls) (span (lambda (x) (not (pred x))) ls))
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(define break! break)
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(define (list-index pred ls . lists)
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(if (null? lists)
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(let lp ((ls ls) (n 0))
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(and (pair? ls) (if (pred (car ls)) n (lp (cdr ls) (+ n 1)))))
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(let lp ((lists (cons ls lists)) (n 0))
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(and (every pair? lists)
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(if (apply pred (map car lists)) n (lp (map cdr lists) (+ n 1)))
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))))
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