Re: 23-less-ac-subst.patch

[Raja R Harinath]

Pavel Roskin <address@hidden> writes:
> On Tue, 23 Jan 2001, Akim Demaille wrote:
> 
> > Index: ChangeLog
> > from  Akim Demaille  <address@hidden>
> >     Don't AC_SUBST too much, as it makes Automake include those
> >     variables in Makefiles, and drives autoscan to require unneeded
> >     programs.
> >
> >     * m4sugar.m4 (m4_expand_once): Let the user specify the witness.
> 
> Witness? I don't understand why you use this word and how it's supposed to
> work.

Witness == "Proof that something was expanded/loaded/substituted".

In Emacs Lisp, the provide/require/featurep triumvirate use a symbol
stored in the 'features' variable as a "witness" to the fact that the
similarly named file has been loaded.

In Autoconf, 'm4_require/m4_provide/m4_provide_if' uses m4 macros that
look like 'm4_provide(foo)' to witness to the fact that the macro
'foo' was expanded.

In either case, a "symbol" that is probably shorter and easier to
compare is used as proof rather than the actual text of the
substitution.

- Hari
-- 
Raja R Harinath ------------------------------ address@hidden
"When all else fails, read the instructions."      -- Cahn's Axiom
"Our policy is, when in doubt, do the right thing."   -- Roy L Ash