[antlr-interest] faster expression parsing

[Austin Hastings]

Terence Parr wrote:
> So, I should have been working on something else but got to thinking 
> about how annoying it is specifying expressions in recursive descent 
> parsers.  You have to have a new rule for each precedence level.  This 
> is also very slow. Just to match 34 it has to descend about 15 method 
> calls.  

I totally agree. (See thread at: 
http://www.antlr.org/pipermail/antlr-interest/2007-December/025112.html)

> I built a prototype single-rule (plus primary and suffix) operator 
> matching thingie today.  I should be able to generate this from some 
> metameta syntax in antlr.  Try it out...it's amazing (v3.1 required 
> due to tree bulding bug fix).

Closer. I want the syntax built in to Antlr. Make expression 
sub-grammars some kind of callable thing.

string_expr:
    @expression_subgrammar { operators = '+', '.', 'x', 'trim'(), 
'ltrim'(), 'rtrim'()  ; }
    ;

=Austin