Ometa is "a new object-oriented language for pattern matching." I've encountered pattern matching in languages like Oz tools to parse grammars like Lexx/Yacc or Pyparsing before. Despite looking at example code, reading discussions, and talking to a friend, I still am not able to get a real understanding of what makes Ometa special (or at least, why some people think it is). Any explanation?
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A:
It's a metalanguage, from what I can tell. You can create new language constructs, and create DSLs; but the most compelling thing is that you can subclass from existing parsers to extend a language. That's what I can remember about it, anyway.
I found this to be interesting: http://www.moserware.com/2008/06/ometa-who-what-when-where-why.html
TraumaPony
2008-09-20 05:34:20
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A:
Also, most important to me, the Squeak port of Ometa allows for left-recursive rules.
From its PEG heritage it gets backtracking and unlimited lookahead. Memoization of previous parse results allows for linear parse times (nearly all the time (*)).
Higher-order productions allow one to easily refactor a grammar.
This paper - Packrat Parsers Can Support Left Recursion - explains the left recursive properties.
(*) Section 5 of the paper explains that one can suffer superlinear parse times, but this problem doesn't manifest in practical grammars.
Frank Shearar
2008-12-10 09:27:12
Presumably you can't have both left recursion and linear parse times, though?
Dominic Cooney
2009-02-16 17:50:45
Yes you can, because of the memoization. Well, most of the time. Section 5 of the paper explains further.
Frank Shearar
2009-02-17 13:02:37