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From: "B. Pym" <Nobody447095@here-nor-there.org>
Newsgroups: comp.lang.lisp,comp.lang.scheme
Subject: Re: MAP (and variants) vs LOOP - Popular opinion observation?
Date: Sun, 8 Sep 2024 12:44:44 -0000 (UTC)
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B. Pym wrote:

> > Then suppose you later need the loop/map to collect some of the values
> > under certain conditions. You might have
> > 
> >    (loop for x in (get-list)
> >          for i from 0
> >          do (format t "~A - ~A~%" i x)
> >          if (test x)
> >          collect (foo x))
> 
> Gauche Scheme
> 
> (use srfi-13)  ;; string-upcase
> 
> (filter-map
>   (lambda (x i)  (print i " - " x)
>     (and (string? x) (string-upcase x)))
>   '(foo "an" 8 "why")
>   (lrange 0))
> 
> 0 - foo
> 1 - an
> 2 - 8
> 3 - why
> ("AN" "WHY")

> Suppose you have
> 
>    (loop for x in (get-list)
>          do (format t "~A~%" x))
> 
> and then it turns out you need to print a numeric index. You can do
> 
>    (loop for x in (get-list)
>          for i from 0
>          do (format t "~A - ~A~%" i x))
> 
> If you start with
> 
>    (mapc (lambda (x) (format t "~A~%" x)) (get-list))
> 
> it seems (to me) that it'd be harder to modify it as needed,
> 
>    (let ((list (get-list)))
>      (mapc (lambda (i x) (format t "~A - ~A" i x))
>            (range 0 (length list))
>            list))
> 
> (I'm assuming the toolkit includes a RANGE utility, or something similar.)

Gauche Scheme

Shorter than the loop:

(for-each
  (pa$  format #t "~a - ~a\n")
  (lrange 0)
  '(a b c))

0 - a
1 - b
2 - c