Yet anothEr Tcl Interpreter - Generate an itcl parser for a BNF-like grammar
Usage example: Parsing C.
CMCc: Converted a YACC grammar to Yeti. It's a really great program - well written and very capable. I'm running into problems, though: how do I use Yeti to parse ambiguous grammars? Yeti doesn't seem to have any equivalent to YACC's %precedence or associativity operators, so it's hard to get it to parse something like `(a * b + x * y)' as ((a *b) + (x * y))
AK: I don't know what Yeti does internally, LL(1), LR(1), LALR(1), ... It might be necessary to disambiguate the grammar to deal with such constructions.
AK, Aug 15: Yeti implements a basic LALR(1) parser. Reduce/Reduce conflicts are resolved via lookahead, shift/reduce conflicts are resolved in favor of shift (seems to be).
In contrast to Yacc and Bison no way to declare operator precedence and associativity information. This information has to be explicitly encoded into the grammar.
References:
IIRC (it's a long time since I looked at the dragon book) some commonly used language constructs (in, say, C) are inherently ambiguous. An example is if/then/else. YACC uses associativity to capture the fact that an else associates with its closest preceding if. CMcC
AK - Sure ? I thought that this was a classic example of a shift/reduce conflict which is solved in favor shifting. I associated (sic) associativity more with expressions and operations in them.
AM Most books I have read about the subject say that if/then/else constructs in C-like languages require some interference with the grammar - that is, the ambiguity needs to be resolved by means outside the theory...