Re: %union foo bar baz and others { ... }

[Paul Eggert]

Akim Demaille <address@hidden> writes:

> I don't know how ANTLR makes the difference between delayed code, and
> immediately executed code, that allows the implementation of something
> like a "cut" to prune the wrong parses.

I'm no ANTLR expert, but I think they put a "?" after the action,
E.g.:

   stat:
           {isTypeName(LT(1))}? ID ID ";"
       |   ID "=" expr ";"
       ;

The lexical analysis of {...}? actions in ANTLR does not seem to
differ from that of ordinary actions.  I'd guess that the same would
be true for Bison; if so, it'll be trivial to add this syntax.  If my
guess is wrong, though, there will be problems of course.


> The SC_AFTER_IDENTIFIER pieces of code is additional code,
> additional burden, that should be removed from Bison.

But this would remove code that supports a POSIX requirement.  Even if
we decided not to conform to POSIX by default (which I don't yet see
the need for, due to backward-compatibility concerns), we would need
to conform if the POSIXLY_CORRECT environment variable is set.  And to
do that, we would need SC_AFTER_IDENTIFIER, or something else equally
complicated.  I don't see any easy way out of this complexity.

Hmm, perhaps you meant to say "SC_PRE_CODE" rather than
"SC_AFTER_IDENTIFER" here?  It seems more relevant here.  To my mind
the SC_PRE_CODE stuff is less defensible than the SC_AFTER_IDENTIFIER
stuff, as it supports something that is not a POSIX requirement, and
it's a worse hack to the lexer.