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From: Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups: comp.std.c
Subject: Re: conditional macro definition also for recursive conditionally limited expansion
Date: Mon, 17 Jan 2022 07:51:06 -0800
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Marco Munari <allerta.it@gmail.com> writes:

> I thought it could be nice to introduce condition inside macro
> definition, to produce less jumping code (so compiler can output
> bigger but more efficient code with concise definition)
>
> a syntax could be defined by adding an optional #defif (due to the
> late time this could be introduced to C, that would be my preference
> reminding to who would learn by seeing it that the if is part of the
> macro definition) as
> #define macro(#N,x) #defif (#N>0) macro(#N-1,?) #defelse ?
>
> usable with macro(5,x)
> expansion parameter that i called #N need to be a constant provided
> to the expansion engine, the # prefix I indicated here is not a
> syntax necessity because it can be deduced by the fact that this
> parameters appears in the #defif condition which also must be fully
> valuable during preprocessing (just a bit more powerful
> preprocessing)  [...]

It's an interesting idea.  There are details that need to be
explored and understood first.  Also I think it would be better
if expanded and generalized, perhaps along the lines of 'cond'
in lisp, or alternatively with ?# :# as preprocessing if/else.
Hmmm...