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Subject: bug#67611: [PATCH] Add a Pcase pattern `cl-lambda` equivalent to
 `cl-destructuring-bind`
Date: Fri, 12 Jan 2024 10:46:43 +0000
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Cc: Okamsn <okamsn@protonmail.com>, 67611@debbugs.gnu.org,
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To: Stefan Monnier <monnier@iro.umontreal.ca>
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On Fri, Jan 12, 2024 at 3:05=E2=80=AFAM Stefan Monnier <monnier@iro.umontre=
al.ca>
wrote:

> I don't think there's a clear enough need for it right now in Emacs core
> to motivate its integration in Emacs proper.  Also, because several
> people have expressed an opinion that leans towards recommending that
> Emacs's own code should probably better avoid using this functionality.

Those people are trying to come up with alternative pattern-matching
libraries which we start to see are not simpler or as powerful
as pcase.

But sure, other pattern-matching libraries exist out there.  See
CL's optima/trivia [1/2] for some very good ones.  Emacs just happens
to have pcase readily available.

> I'd be quite happy to include such a think in GNU ELPA, OTOH.

Could be, but why really?  Why are CL things which rest on such
high-quality well-known designs, older than many things Emacs,
relegated to a place where they're less discoverable?

Here, I think at least the new fresh implementation of
lambda-list parsing (which is the meat-and-bones of this patch)
is worth taking a look at.

It's the function 'cl--pcase-cl-lambda-var-groups'.

I would definitely consider grooming this function, renaming
it, and keeping it in core, exposing to general Elisp usage
in cl-macs.el (or cl-lambdalist.el, cl-ll.el), even if a new
pcase pattern that uses it goes to ELPA (but why, really?)

That util could help us write other lambda-list destructuring
alternatives that understand &optional, &rest.  Because with or
without it, we already use a lot of the &optional, &rest explicitly
in Emacs.  And we also use &key and &allow-other-keys in many other
places, though sometimes in ad-hoc lets-not-call-this-bull-by-its-name
fashion.

IOW there is no general purpose-util like Alexandria's
'parse-ordinary-lambda-list', and this could be it.  It could
not only be used to simplify and add coherence to many of these
existing compile-time structures, for example helping simplify
things and address FIXMEs in cl-lib.el.

Jo=C3=A3o

[1] https://github.com/m2ym/optima
[2] https://github.com/guicho271828/trivia

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<div dir=3D"auto">On Fri, Jan 12, 2024 at 3:05=E2=80=AFAM Stefan Monnier &l=
t;<a href=3D"mailto:monnier@iro.umontreal.ca" target=3D"_blank" rel=3D"nore=
ferrer">monnier@iro.umontreal.ca</a>&gt; wrote:<br>
<br>
&gt; I don&#39;t think there&#39;s a clear enough need for it right now in =
Emacs core<br>
&gt; to motivate its integration in Emacs proper.=C2=A0 Also, because sever=
al<br>
&gt; people have expressed an opinion that leans towards recommending that<=
br>
&gt; Emacs&#39;s own code should probably better avoid using this functiona=
lity.<br>
<br>
Those people are trying to come up with alternative pattern-matching<br>
libraries which we start to see are not simpler or as powerful<br>
as pcase.<br>
<br>
But sure, other pattern-matching libraries exist out there.=C2=A0 See<br>
CL&#39;s optima/trivia [1/2] for some very good ones.=C2=A0 Emacs just happ=
ens <br>
to have pcase readily available.<br>
<br>
&gt; I&#39;d be quite happy to include such a think in GNU ELPA, OTOH.<br>
<br>
Could be, but why really?=C2=A0 Why are CL things which rest on such<br>
high-quality well-known designs, older than many things Emacs,<br>
relegated to a place where they&#39;re less discoverable?<br>
<br>
Here, I think at least the new fresh implementation of<br>
lambda-list parsing (which is the meat-and-bones of this patch)<br>
is worth taking a look at.<br>
<br>
It&#39;s the function &#39;cl--pcase-cl-lambda-var-groups&#39;.<br>
<br>
I would definitely consider grooming this function, renaming<br>
it, and keeping it in core, exposing to general Elisp usage<br>
in cl-macs.el (or cl-lambdalist.el, cl-ll.el), even if a new<br>
pcase pattern that uses it goes to ELPA (but why, really?)<br>
<br>
That util could help us write other lambda-list destructuring<br>
alternatives that understand &amp;optional, &amp;rest.=C2=A0 Because with o=
r<br>
without it, we already use a lot of the &amp;optional, &amp;rest explicitly=
<br>
in Emacs.=C2=A0 And we also use &amp;key and &amp;allow-other-keys in many =
other<br>
places, though sometimes in ad-hoc lets-not-call-this-bull-by-its-name<br>
fashion.<br>
<br>
IOW there is no general purpose-util like Alexandria&#39;s<br>
&#39;parse-ordinary-lambda-list&#39;, and this could be it.=C2=A0 It could<=
br>
not only be used to simplify and add coherence to many of these<br>
existing compile-time structures, for example helping simplify<br>
things and address FIXMEs in cl-lib.el.<br>
<br>
Jo=C3=A3o<br>
<br>
[1] <a href=3D"https://github.com/m2ym/optima" rel=3D"noreferrer noreferrer=
" target=3D"_blank">https://github.com/m2ym/optima</a><br>
[2] <a href=3D"https://github.com/guicho271828/trivia" rel=3D"noreferrer no=
referrer" target=3D"_blank">https://github.com/guicho271828/trivia</a><br><=
/div>

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