XPost: comp.lang.scheme

Fred Gilham wrote:

For those who are interested, here are two versions of the
`every-other' function we were discussing a couple months ago, done
for amusement value with the SERIES package that was mentioned
recently:

(defun every-other (list &key (start 0))
(collect
(choose (series t nil)
(scan (nthcdr start list)))))

This one uses SERIES to create a series of (t nil t nil ...); CHOOSE
uses this series to determine whether or not to take the current item
from the series created from the original list by SCAN. This was the

Gauche Scheme

(use srfi-1) ; circular-list

(define (every-other lst)
(filter-map
(cut and <> <>)
(circular-list #t #f)
lst))

(every-other (iota 22))
===>
(0 2 4 6 8 10 12 14 16 18 20)

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