[antlr-interest] Re: more lexical determinism
Sinan
sinan.karasu at boeing.com
Thu Dec 6 10:04:01 PST 2001
howardckatz wrote:
>
> This has been an interesting exercise. I can see that this particular
> problem -- where two tokens consist of closely overlapping character
> sets -- is one that antlr doesn't handle that well. I can see one
> other approach that might work -- sticking some string-parsing Java
> code of my own either into the parser grammar or maybe in a
> downstream TokenStream. Time to play I guess ...
>
yacc/lex won't either.
what you should do really is
assume a could have '_' and b can't.
then you really have something like
rule : (a | b) COLON b;
so in lexer you say
B : ( LETTER | DIGIT | '_' { set type to A})+;
in parser
rule: (A | B) COLON B;
or pushing into other rules
rule : id COLON word ;
id : A | B;
word : B;
Sinan
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