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Re: defmacro with built-in gensym declaration and initialization

From: Basil L. Contovounesios
Subject: Re: defmacro with built-in gensym declaration and initialization
Date: Thu, 21 Jan 2021 21:23:59 +0000
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/28.0.50 (gnu/linux)

Stefan Monnier <monnier@iro.umontreal.ca> writes:

>>> Sorry, I suspect I misunderstood.  What's a native arglist?  Doesn't
>>> defmacro already have native support for &optional and &rest keywords?
>> Yes, and that's what I mean by native arglists - the ones possessed by
>> built-in C objects such as subroutines, lambda expressions, compiled
>> code, dynamic module functions, etc. and used by built-in C functions
>> such as funcall.
>> By contrast, cl-defmacro, other CL compatibility definitions, etc. have
>> to parse a plain Elisp arglist for CL-specific features like &aux.
> FWIW, `defmacro` is itself a macro, just like `cl-defmacro`, so it
> wouldn't be that terribly hard (the only problem is that it needs to be
> implemented without itself using macros, more or less).

Oh, right.

> For me it's more a question that whatever something like `&gensym` can't
> use values that are computed during the macro expansion, , so
>     (defmacro M (ARGS &gensym FOO)
>       ...)
> is equivalent to something like:
>     (defmacro M (ARGS)
>       (with-gensyms (FOO)
>         ...))
> except:
> - it's a bit more concise
> - it exposes internal implementation details into the arglist, which is
>   usually considered as part of the signature.
> - it doesn't cover the cases where you need `with-gensyms` deeper than
>   at the toplevel of the macro's body.
> I find the added concision doesn't pay for the other two downsides.



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