GNU bug report logs - #58278
Add new function seq-keep

Previous Next

Full log

Message #41 received at 58278 <at> debbugs.gnu.org (full text, mbox):

From: Lars Ingebrigtsen <larsi <at> gnus.org>
To: Jonas Bernoulli <jonas <at> bernoul.li>
Cc: 58278 <at> debbugs.gnu.org
Subject: Re: bug#58278: Add new function seq-keep
Date: Tue, 04 Oct 2022 15:47:16 +0200

Jonas Bernoulli <jonas <at> bernoul.li> writes:

> Yes, that would be an improvement.  Some (but certainly not all)
> uses of dash's `-keep' look something like
>
>   (-keep (lambda (elt)
>            (and (symbolp elt)
>                 (symbol-name elt)))
>          sequence)
>
> and
>
>   (seq-keep #'symbol-name sequence #'symbolp)
>
> would be much nicer in those situations.

Hm...  That's not exactly what I was thinking here.  I was thinking

(cl-defgeneric seq-keep (func sequence &optional pred)
  (if pred
      (seq-filter pred (seq-mapcar func sequence))
    (delq nil (seq-mapcar func sequence))))

which is the traditional "keep" semantics, but allows extending the
concept of "keep" to more than "is non-nil".

But that may well be an overcomplication -- in the unusual cases where
it's not nil that people want to keep, they can just type

  (seq-filter pred (seq-mapcar func sequence))

themselves, which has very clear semantics.

So I think, on second consideration, I'd rather just go with

(cl-defgeneric seq-keep (func sequence)
  (delq nil (seq-mapcar func sequence)))

like you originally suggested (but with just an argument name change).

Previous Next

GNU bug tracking system
Copyright (C) 1999 Darren O. Benham, 1997,2003 nCipher Corporation Ltd, 1994-97 Ian Jackson.