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(reduce, reduce-right): Don't call f with ridentity, use

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it only if lst is empty, per srfi and intended optimization reduce
represents over fold.
This commit is contained in:
Kevin Ryde 2005-02-11 21:37:08 +00:00
parent 8ff017428d
commit b064377679
1 changed files with 6 additions and 2 deletions
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8
srfi/srfi-1.scm
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@ -511,10 +511,14 @@
(uf (g seed) (cons (f seed) lis)))))) (uf (g seed) (cons (f seed) lis))))))
(define (reduce f ridentity lst) (define (reduce f ridentity lst)
(fold f ridentity lst)) (if (null? lst)
ridentity
(fold f (car lst) (cdr lst))))
(define (reduce-right f ridentity lst) (define (reduce-right f ridentity lst)
(fold-right f ridentity lst)) (if (null? lst)
ridentity
(fold-right f (last lst) (drop-right lst 1))))
;; Internal helper procedure. Map `f' over the single list `ls'. ;; Internal helper procedure. Map `f' over the single list `ls'.