[antlr-interest] New user
glindholm at yahoo.com
Thu Aug 29 09:56:55 PDT 2002
A couple other important points about predicates:
- Semantic predicates are written in the host language (Java, C++,
etc.) and provide a break-out hook at that point in the parsing.
You have full access to the internals of the parser plus access
to symbol tables and any external resources you've setup.
- Syntactic predicates are written in and use the "syntax" grammer
of the parser to provide unlimited look ahead.
- Syntactic predicates are used to select between one of several
alternatives (usually with a common prefix)
- Syntactic predicates are "ordered" they are checked in the order
that they are written in. I believe this is the only way to do
an ordered series of tests.
--- mzukowski at yci.com wrote:
> 5. When do I use syntatic predicate and semantic predicate? Why does
> semantic make sense: ( set_clause ) => set_clause ??!!
> It doesn't make sense like that because you're not using it in
> What it is saying is choose this alternative if the syntactic
> matches. Sometimes you have things that need "infinite
> can't always decide in "k" tokens what is happening. When you have
> situation you use a syntactic predicate. Semantic predicates are for
> like checking symbol tables--the actual semantics of the program.
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