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Added (list-insert!)

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Justin Ethier 2015-05-22 01:16:52 -04:00
parent 4e4eff037e
commit 91d8a981fb
1 changed files with 14 additions and 0 deletions
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14
scheme/cyclone.scm
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@ -46,3 +46,17 @@
(new-tail (recur (delete x tail))))
(if (eq? tail new-tail) lis (cons x new-tail)))))
(recur lis))
;; Insert obj at index k of list, increasing length of list by one.
(define (list-insert! lis k obj)
(cond
((null? lis) (error "list-insert, lis cannot be null"))
((and (> k 0) (null? (cdr lis)))
(set-cdr! lis (cons obj '())))
((zero? k)
(let ((old-car (car lis)))
(set-car! lis obj)
(set-cdr! lis (cons old-car (cdr lis)))))
(else
(list-insert! (cdr lis) (- k 1) obj))))