Re: Semantics make a grammar ambiguous

Bill A wrote in message
>[..]
>I'm having difficulty parsing this with an LALR parser (generated from
>a parser generator) because the second str should be an id but matches
>a typedef definition so a typedef terminal is returned from the lexer.
>What is the traditional way to handle this ambiguity? Is this a good
>case of why most production compilers are recursive decent?


To solve this problem I allow a typedef-name as well as an identifier
to appear in a declaration. I have written separate non-terminals for
declarations that allow redeclaring of a typedef-name and for ones
that don't. Each non-terminal has to be used selectively in the
context in order to avoid conflicts (for example you can't redeclare a
typedef-name in a declaration with implicit type). After quite a lot
of head-scratching now there is only one shift-reduce conflict in the
grammar.


I don't think it is a good idea to feed the scanner with context-dependent
information - it could cause troubles with error recovery and generally I
think it could introduce obscure bugs.


regards,
Tzvetan

Return to the comp.compilers page.
Search the comp.compilers archives again.