Re: M4 syntax $11 vs. ${11}

[Paul Eggert]

Eric Blake <address@hidden> writes:

> Because I was hoping that M4 2.0 could borrow a leaf from shell parsing,
> and ALSO implement things like ${1-default} that is more compact than the
> current ifelse(`$1',,`default',`$1') in M4 parlance.

Sure, but doesn't that just delay the conversion problem?  The price
will eventually have to be paid for having a syntax that is so close
to the shell's.

How about if M4 uses a slightly-different syntax, so that the two uses
are never confused?  That way, the conversion problem won't ever have
to be addressed, and Autoconf won't have to disable the extension
during a transition period.

So, for example, suppose M4 uses the syntax ${{11}} to refer to
argument 11?  Or (if you prefer something shorter) ${+11}?  An
advantage to this sort of approach is that it gives you more leeway
for future extensions.