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From: "B. Pym" <Nobody447095@here-nor-there.org>
Newsgroups: comp.lang.lisp,comp.lang.scheme
Subject: Re: novice: mapcan use?
Date: Wed, 11 Sep 2024 01:44:56 -0000 (UTC)
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Pascal Costanza wrote:

> > I have used NRECONC.  When you are processing a list and the
> > interesting stuff is at the head of the list, you write a loop like
> > this:
> >
> >   (do ((tail      list (cdr tail))
> >        (processed '()  (cons (do-something (car tail))
> >                              processed)))
> >       ((done? ...) (nreconc processed tail)))
> >
> > The nreconc reverses the processed stuff (which is accumulated
> > backwards) and pastes it on to the remaining element of LIST.
> 
> Ah, finally a clue. Thanks for that!
> 
> Indeed, I could have used something like that before, but came up with a
> solution with LOOP that looks like this:
> 
> (loop for (car . cdr) on list
>        collect (do-something car) into processed
>        until done
>        finally (return (nconc processed cdr)))

Gauche Scheme

(use srfi-1)  ;; span

(receive (nums rest) (span number? '(2 3 4 a b c))
  (append (map square nums) rest))
  ===>
(4 9 16 a b c)


(lope dolist-by x xs cdr '(2 3 4 a b c)
  until (not (number? x))
  collect-in (sqr x) processed
  returning (append processed xs))

===>
'(4 9 16 a b c)