srfi-1 reduce

srfi-1 reduce

[Kevin Ryde]

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        * srfi-1.scm (reduce, reduce-right): Don't call f with ridentity, use
        it only if lst is empty, per srfi and intended optimization reduce
        represents over fold.


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--- srfi-1.scm.~1.48.~	2005-02-01 10:06:05.000000000 +1100
+++ srfi-1.scm	2005-02-11 21:11:00.000000000 +1100
@@ -511,10 +511,14 @@
 	  (uf (g seed) (cons (f seed) lis))))))
 
 (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)
-  (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'.

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