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From: "B. Pym" <Nobody447095@here-nor-there.org>
Newsgroups: comp.lang.lisp,comp.lang.scheme
Subject: Re: sum over list?
Date: Tue, 17 Sep 2024 13:45:13 -0000 (UTC)
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Frode Vatvedt Fjeld wrote:

> > (sum '(2 3 4)) => 9
> > (sum '(5 6)) => 11
> 
> The usual way of doing this would be
> 
>   (reduce #'+ '(2 3 4))
> 
> which is considered to be preferable to using APPLY. LOOP can do the
> job almost as well:
> 
>   (loop for x in '(2 3 4) sum x)
> 
> The thing about LOOP is that it's much more flexible, in case you need
> some slight variation of the theme, like for example:
> 
>   (loop for x in '(2 3 a 4) when (numberp x) sum x)


Gauche Scheme

(use gauche.lazy) ;; lfilter [lazy filtering]

(fold + 0 (lfilter number? '(2 3 a 4)))