Re: predicate parsing

Re regarding predicate parsing:


What exactly are predicates? I've had a look at the *excellent* PCCTS
which uses predicates, but I don't see how they can help very much. I'm
trying to write a C++ parser (something simple to start with :-)), but
predicate parsing would have to look-ahead many tokens to decipher
ambiguities wouldn't it?


I wrote a backtracking LALR parser which basically recursively 'trial'
parses (similar method to Gary Merrill, but trial parsing is specified
with the grammar). I've managed to get it to parse almost all C++,
including templates and exceptions, but it's pretty big (>950states). I
also needed error repair which is why I **had** to write my own parser.


I'd have liked to use LL since it is much easier to understand but seemed
to run into so many problems. Firstly, I wanted it to be as fast as
possible. I can write the parser driver in assembler to read the tables.
Second, I needed error repair. LL parsers seem to have a hard-time
repairing errors. Thirdly, I couldn't parse-out those lovely ambiguities
in C++ :-).




.. So, would predicates help or what? Are they for simpler things?




--
James Huntington
Software Interrupt Developments, Leeds, UK.
--

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