From Newsgroup: comp.lang.scheme
B. Pym wrote:
B. Pym wrote:
B. Pym wrote:
You have a list contain both strings and numbers.
Generate a new list in which the adjacent strings
have been concatenated.
Scheme
(define (merge-strings List)
(reverse
(fold
(lambda (e accum)
(if (and (string? e) (pair? accum) (string? (car accum)))
(cons (string-append (car accum) e) (cdr accum))
(cons e accum)))
'()
List)))
(merge-strings '("1" "2" 3 4 "5" "6" 7 8 "9"))
===>
("12" 3 4 "56" 7 8 "9")
(defun merge-strings (list)
(loop while list
if (stringp (car list)) collect
(apply #'concatenate 'string
(loop while (stringp (car list))
collect (pop list)))
else collect (pop list)))
Gauche Scheme
;; Doesn't cause an error is list is empty.
(define (car~ xs) (and (pair? xs) (car xs)))
(define (merge-strings xs . r)
(while (pair? xs)
(push! r
(if (string? (car xs))
(let f ()
(if (string? (car~ xs)) (string-append (pop! xs) (f)) ""))
(pop! xs))))
(reverse r))
Shorter.
(define (merge-strings List)
(fold-right
(^(e accum)
(cons
(if (and (string? e) (string? (car~ accum)))
(string-append e (pop! accum))
e)
accum))
()
List))
Shorter.
(define (merge-strings List)
(fold-right*
(^(e accum both)
(cons
(if (every string? both)
(string-append e (pop! accum))
e)
accum))
()
List))
Given:
(define (fold-right* kons knil xs)
(fold-right
(lambda (e accum)
(if (pair? accum)
(kons e accum (list e (car accum)))
(kons e accum (list e #f)))
)
knil
xs))
--
[T]he problem is that lispniks are as cultish as any other
devout group and basically fall down frothing at the mouth if
they see [heterodoxy]. --- Kenny Tilton (05 Dec 2004)
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