GNU bug report logs - #19371
25.0.50; doc of functions and macros defined in macroexp.el

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From: Michael Heerdegen <michael_heerdegen <at> web.de>
To: Lars Ingebrigtsen <larsi <at> gnus.org>
Cc: 19371 <at> debbugs.gnu.org, Drew Adams <drew.adams <at> oracle.com>
Subject: bug#19371: 25.0.50; doc of functions and macros defined in macroexp.el
Date: Sat, 03 Aug 2019 00:33:14 +0200

Lars Ingebrigtsen <larsi <at> gnus.org> writes:

>  (defun macroexp-progn (exps)
> -  "Return an expression equivalent to \\=`(progn ,@EXPS)."
> +  "Return EXPS with `progn' prepended.
> +If EXPS is a single expression, `progn' is not prepended."
>    (if (cdr exps) `(progn ,@exps) (car exps)))

That's described a bit confusingly: AFAIU EXPS should always be a list
of expressions, and when it's _a_list_ of only one expression, `progn'
is not prepended and the expression is returned (and not EXPS as your
text suggests).  BTW, compared to that description I find the original
version much better (simpler).

> > 2. And then there is `macroexp-let2*', whose doc string says only to
> > bind each binding (bind a binding?!) "as `macrolet2' does".  That
> > means nothing.  Presumably, based on the `*' in the name, the behavior
> > is similar to that of `let*'.  If so, you can use the doc of `let*
> > as inspiration.
>
> Uhm...  I have no idea what it does:
>
> (defmacro macroexp-let2* (test bindings &rest body)
>   "Bind each binding in BINDINGS as `macroexp-let2' does."
>   (declare (indent 2) (debug (sexp (&rest (sexp form)) body)))
>   (pcase-exhaustive bindings
>     ('nil (macroexp-progn body))
>     (`((,var ,exp) . ,tl)
>      `(macroexp-let2 ,test ,var ,exp
>         (macroexp-let2* ,test ,tl ,@body)))))

You understand what macroexp-let2 does?  It supports one binding (a var
plus an expression, specified as separate arguments).  macroexp-let2*
supports a list of such pairs specified as BINDINGS, similar to let*.

The naming scheme `macroexp-let2' vs. `macroexp-let2*' is not ideal:
first, because `macroexp-let2' doesn't support multiple bindings like
`let', and secondly because, if I look at the use cases in the sources,
most of them just want to establish multiple bindings, but parallel
binding would suffice, so they actually want to non-stared version of
macroexp-let2*, which is not macroexp-let2 - AFAICT it doesn't exist.

Michael.

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