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antlrcontext-free-grammarjavacc

ANTLR syntactic predicates for JAVACC

In ANTLR, we can use syntactic predicates to solve certain issues as follows. This is just a simple example.

a : (L K)=> b
   | c
   ;

b : L K
   ;

c : L M
   ;

What I want to know is how to achieve the same thing in JAVACC? Thanks.

Solution

  • There is a concept called SYNTACTIC LOOKAHEAD in javacc. You can use that to achieve same behavior.

    For an example assume your grammar rule is as follows. void Expr(): {} { Call () | Var() }

    If you need to do a lookahead of unknown times then you can for something like

    void Expr():
{}
{
LOOKAHEAD(Call())
Call () | Var()
}

    For more information please refer http://javacc.java.net/doc/lookahead.html