bug#33309: Add flatten-list?

[Alex Branham <alex.branham@gmail.com>]

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On Wed 07 Nov 2018 at 14:36, Drew Adams <drew.adams@oracle.com> wrote:

> FWIW, I don't think Emacs Lisp needs a flatten
> function.
>
> 1. Even Common Lisp doesn't bother with one.
>    (And there are lots of Common Lisp
>    functions I'd sooner see added to Emacs.)
>
> 2. It's trivial to define when needed, and
>    there are not a lot of existing uses of it.

Like I said, there's at least four implementations in Emacs of the same
thing, and who knows how many in 3rd-party packages in ELPA or
elsewhere. I'm not sure what you consider "a lot," but DRY kicks in
around three times for me.

> 3. The functions you mention do not all behave
>    the same.  Even their arg lists are not the
>    same.  (But sure, they could all be made to
>    use a common version, if that were important.)
>
> 4. (flatten-list 42) => (42)
>
>    The doc string says nothing about the case
>    where the argument LIST (a bad name here)
>    is not a list.  And if the arg need not be
>    a list then "-list" in the function name
>    is not good.

Right, I didn't mean to imply that the one I sent be added in its
current state. I just meant to kick off discussion. I basically
copy/pasted it from somewhere (lpr, I think?). If added it'll need to be
properly documented and perhaps message-flatten-list and the others made
obsolete aliases.

Thanks,
Alex

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