Re: YACC with infinite lookahead

Daniele Benegiamo asked:


> Someone know if there exists a version of YACC with infinite lookahead?
>
> I'm writing a compiler for a new language and I have found that LALR(1)
> implemented by Yacc needs too adjustments in the grammar that make it
> too unreadable.
>
> I have tried to use PCCTS but his syntax is too complex and the problem
> of readability is not resolved. Instead the syntax of Yacc is ok but
> have the lookahead problem.


As of 2.3 (or perhaps it was 2.2) Yacc++(R) supports syntactic
predicates for infinite lookahead (via controlled backtracking). The
rest of the notation is essentially yacc extended with regular
expressions. Note that it is a commercial product and not public
domain, free software, or shareware though.


Visual Parse++ has a "natural language" mode that appears to be
Tomita/Lang style parsing (simulating an Earley parser using LR tables
and generating "shared parse forests"). Again, it is a commercial
product.


The tool Btyacc applies backtracking rules to yacc grammars to achieve
"infinite lookahead". I don't remember whether it is commercial or not.


Disclaimer, I helped write Yacc++.


Hope this helps,
-Chris


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