RFC: new changeresyntax builtin

[Gary V. Vaughan]

I'm thinking of removing epatsubst, eregexp and erenamesyms in HEAD, in
favour of a more flexible and scalable changeresyntax builtin as an
analogue to re_set_syntax in the GNU regex C API.

Rather than implement the full 2 dozen or so RE_CONTEXT_INDEP_ANCHORS
and friends along with a mini-parser to OR together all the relevant
bits, I think just the high level settings might be sufficient, with
the added clarity of being a set of mutually exclusive options.
With that in place, one could do:

  changeresyntax(`GNU_AWK')

or:

  changeresyntax(`POSIX_EXTENDED')

and to reset to the default (m4-1.4.x patsubst/regexp syntax):

  changeresyntax(`EMACS')

or:

  changeresyntax()

If a bogus operand is given:

  changeresyntax(`meh')
  => stdin:1: m4: ERROR: unknown argument to built-in `changeresyntax';
     use one of: AWK, ED, EGREP, EMACS, GNU_AWK, GREP, POSIX_AWK, POSIX_BASIC, 
POSIX_EGREP, POSIX_EXTENDED, SED.

This replaces 3 builtins with one more powerful builtin, an obvious
win to my mind :-)  Can anyone see a downside to this change?

Cheers,
        Gary.
-- 
Gary V. Vaughan      ())_.  address@hidden,gnu.org}
Research Scientist   ( '/   http://blog.azazil.net
GNU Hacker           / )=   http://trac.azazil.net/projects/libtool
Technical Author   `(_~)_   http://sources.redhat.com/autobook

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