flex or reflex

Hi,

I am willing to update our flex in base, my first motivation is to be able to
have reentrant lexer in base, I first went to the http://flex.sourceforge.net
derivative from flex 2.5.4, I've imported it in contrib, and I'm able to build
the whole base using the 2.5.35 version (almost vanilla) and with just one or
two small fixes from from .l files (mostly adding %option nounistd to fix
warnings) One of the major "problem" of this version is that it uses m4 (it is
compatible with our m4 version in base - the recently updated one).

Another alternative is to use reflex
(http://www.invisible-island.net/reflex/reflex.html) which seems a good one
because, it is more respectful of the POSIX lex unfortunately it doesn't seem to
be able to create reentrant lexer.

Given this, I think it is better for us to choose flex.

Of course it is still possible to add reentrant feature to our flex, but it
would be more painful.

After this I plan to import byacc
http://www.invisible-island.net/byacc/byacc.html which can generate reentrant
parser.

regards,
Bapt