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[bugfix] circular-list? in srfi-1 

circular-list? does not get stuck in an infinite loop if it is given a list such as '(1 2 3 2 3 2 3 2 3 ...).
This commit is contained in:
koba-e964 2014-03-17 10:43:39 +09:00
parent 21b17cfd59
commit dfb525157e
1 changed files with 8 additions and 11 deletions
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19
piclib/srfi/1.scm
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@ -51,19 +51,16 @@
;; list=
(define (not-pair? x)
(not (pair? x)))
;; detects circular list using Floyd's cycle-finding algorithm
(define (circular-list? x)
(and (pair? x)
(let rec ((lst (cdr x)))
(cond ((not-pair? lst) #f)
((null? lst) #f)
((eq? x lst) #t)
(else (rec (cdr lst)))))))
(let rec ((rapid x) (local x))
(if (and (pair? rapid) (pair? (cdr rapid)))
(if (eq? (cddr rapid) (cdr local))
#t
(rec (cddr rapid) (cdr local)))
#f)))
;; if list? is support circular list, (define proper-list? list?)
(define (proper-list? x)
(if (not (circular-list? x))
(list? x)))
(define proper-list? list?)
(define (dotted-list? x)
(and (pair? x)