Re: defmacro with built-in gensym declaration and initialization

[akater <nuclearspace@gmail.com>]

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"Basil L. Contovounesios" <contovob@tcd.ie> writes:

> IMO, this minor convenience is insufficient motivation for
> conflating/complicating a macro's global arglist, i.e. its arity,
> calling convention, etc., with utilities for its local body.  Is there
> some other motivation?  Am I missing something?

My motivation mostly comes from CL where complicated lambda lists are
not considered an issue, and it didn't come to my mind it could be an
issue for Emacs Lisp users.  In particular, &gensym does indeed follow
the design of &aux, described below as “hideous” (another surprise).  I
use &aux regularly, and I find it a nice addition as it reduces the
nesting depth of defun and defmacro forms.  &gensym does that and saves
some boilerplate on top of it, I tried it in real life macros, found it
useful, and that's pretty much it.

> conflating/complicating a macro's global arglist, i.e. its arity,

What's the arity of defmacro?  This form already allows any number of
arguments so as far as I can see adding another keyword does not change
arity.  Calling convention is backwards compatible.  Again, Common Lisp
implementations are allowed to introduce their own lambda list keywords
so I didn't (and still don't) think extending lambda-list keywords set
is a big deal.

> Why not provide handy gensym/once-only local conveniences for macro
> authors instead (some of which already exist in one form or another,
> e.g. macroexp-let2, inline-letevals, and org-with-gensyms)?

I don't have much experience with macroexp-let2 which on the first
glance looks like an overcomplicated once-only that is mostly relevant
for functions that are meant to be byte-compiled.  Since we're moving to
natively compiled Elisp, I was thinking it's going to become less
relevant in near future, and &gensym covers most use cases of once-only.

Again, org-with-gensyms is precisely something that's being replaced
here with an alternative that is less verbose and has a decreased
nesting depth.

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