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Fixed PR 7650.

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iota now uses (+ start (* n step)) to calculate the elements, instead of successive subtractions.

svn: r6025
This commit is contained in:
Jens Axel Soegaard 2007-04-23 19:43:43 +00:00
parent 940d100b2d
commit a5550a69da
1 changed files with 12 additions and 9 deletions
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21
collects/srfi/1/cons.ss
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@ -98,15 +98,18 @@
;; IOTA count [start step] (start start+step ... start+(count-1)*step)
(define iota
(opt-lambda (count [start 0] [step 1])
(check-arg integer? count 'iota)
(check-arg number? start 'iota)
(check-arg number? step 'iota)
(let ((last-val (+ start (* (- count 1) step))))
(do ((count count (- count 1))
(val last-val (- val step))
(ans '() (cons val ans)))
((<= count 0) ans)))))
(opt-lambda (count [start 0] [step 1])
(check-arg integer? count 'iota)
(check-arg number? start 'iota)
(check-arg number? step 'iota)
(unless (or (zero? count) (positive? count))
(error 'iota "count expected to be non-negative, got: ~a" count))
(let loop ([n 0])
(cond
[(= n count) '()]
[else (cons (+ start (* n step))
(loop (add1 n)))]))))
)