Path: ...!3.eu.feeder.erje.net!feeder.erje.net!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail
From: "B. Pym" <No_spamming@noWhere_7073.org>
Newsgroups: comp.lang.lisp
Subject: remove-elements-not-satisfying-the-predicate
Date: Wed, 3 Jul 2024 00:42:32 -0000 (UTC)
Organization: A noiseless patient Spider
Lines: 33
Message-ID: <v626pj$1rui7$1@dont-email.me>
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Injection-Date: Wed, 03 Jul 2024 02:42:32 +0200 (CEST)
Injection-Info: dont-email.me; posting-host="1439b84b29baa786e04afeccb1cf6774";
	logging-data="1964615"; mail-complaints-to="abuse@eternal-september.org";	posting-account="U2FsdGVkX1+SVx8Uf1H3ptwswR4JP5h0"
User-Agent: XanaNews/1.18.1.6
Cancel-Lock: sha1:x5OxM6Hb5eMRw9kKyH7EITaTIPE=
Bytes: 1866

Barry Margolin wrote:

> In article ... (Christopher Dollin) writes:
> >So suppose someone says "please implement 'remove-if-not'. I would like
> >your solution to generate no garbage if possible and to be reasonably
> >efficient".
> 
> Here's a version I threw together quickly (note that it doesn't take
> any options as the CL version does, and it only accepts a list, not
> any sequence):
> 
> (defun simple-remove-if-not (test list)
>   (let ((result nil))
>     (dolist (item list)
>       (unless (funcall test item)
>         (push item result)))
>     (nreverse result)))

What an egregiously bad name: "remove-if-not"
Scheme uses the sensible "filter".

* (remove-if-not 'oddp '(0 2 3 5))

(3 5)

* (simple-remove-if-not 'oddp '(0 2 3 5))

(0 2)

See?  The high and mighty CL (COBOL-like) guru got it wrong.
Of course, he probably didn't test it.  He has said that
he doesn't have CL (COBOL-like) installed on his computer.
It's not worth installing.