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42 lines
1.2 KiB
Scheme
42 lines
1.2 KiB
Scheme
;; predicates.scm -- list prediates
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;; Copyright (c) 2009 Alex Shinn. All rights reserved.
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;; BSD-style license: http://synthcode.com/license.txt
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(define (proper-list? x)
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(cond ((null? x) #t)
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((pair? x) (proper-list? (cdr x)))
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(else #f)))
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(define (circular-list? x)
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(and (pair? x) (pair? (cdr x))
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(let race ((hare (cdr x)) (tortoise x))
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(or (eq? hare tortoise)
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(and (pair? hare) (pair? (cdr hare))
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(race (cddr hare) (cdr tortoise)))))))
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(define (dotted-list? x)
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(not (proper-list? x)))
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(define (not-pair? x) (not (pair? x)))
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(define (null-list? x) (null? x)) ; no error
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(define (list= eq . lists)
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(let lp1 ((lists lists))
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(or (null? lists)
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(null? (cdr lists))
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(let lp2 ((ls1 (car lists)) (ls2 (cadr lists)))
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(if (null? ls1)
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(and (null? ls2)
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(lp1 (cdr lists)))
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(and (eq (car ls1) (car ls2))
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(lp2 (cdr ls1) (cdr ls2))))))))
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(define (length+ x)
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(if (not (pair? x))
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0
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(let lp ((hare (cdr x)) (tortoise x) (res 0))
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(and (not (eq? hare tortoise))
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(if (pair? hare)
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(lp (cddr hare) (cdr tortoise) (+ res 1))
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res)))))
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