From Newsgroup: comp.lang.lisp
B. Pym wrote:
Kent M. Pitman wrote:
Even non-programmers know
what it means to say "For every setting at the table, make sure the napkin is arranged right".
This can be expressed functionally in Scheme using map (like mapcar in CL).
It's not necessary to use iteration.
But MAP is not good for expressing "For every number from 0 to 9, make sure
it appears on the phone dial" because Scheme does not provide an object over which one can "map" numeric ranges, as CL's LOOP does.
Gauche Scheme:
(define phone-dial '(0 1 2 3 4 5 6 7 8 9))
(every (cut member <> phone-dial) (iota 10))
===>
(9)
(every (cut member <> phone-dial) '(2 6 8 22))
===>
#f
(find (lambda(x) (not (member x phone-dial))) '(2 6 8 22))
===>
22
(use srfi-1)
(lset-difference = '(2 6 8 22) phone-dial)
===>
(22)
Using "is":
(every (is member phone-dial) (iota 10))
Given:
(define is
(case-lambda
[(x) (lambda(y) (equal? y x))]
[(pred x) (lambda(y) (pred y x))]
[(key pred x) (lambda(y) (pred (key y) x))]))
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