[antlr-interest] antlr - sub ast tree

[Alessandro Leonardi]

Hi,

 

I'm working about an existing antlr grammar.

 

I'm using java.

 

In the Tree Parser Class are defined 2 method:

expr and exprs

 

 

class ExpressionTreeWalker extends TreeParser;

.

expr  returns [double r]

.

strs returns [String r]

.

 

Expr implements the ast evalutation on numeric operators, Strs on string
operators.

 

Some AST subtree nodes should be calculated by expr and some others by strs
but if I use this syntax, 

 

    CommonAST parseTree = (CommonAST) this.getAST();

    ExpressionTreeWalker walker = new ExpressionTreeWalker();

    String r = walker.expr(parseTree);

 

all tree will be evaluated by expr method.

How is possible to force the ast evaluation to use strs to traverse a
particular subtree?

 

Example: 

 

..

relExpression:

   expr ^EQ expr

 

.

 

tokens {

..

EQ:"="

..

}

 

class ExpressionTreeWalker extends TreeParser;

.

 

  expr returns [double r]

  { double  a,b; r=0; String str,str1,str2; 

  }

#EQ (a=expr b=expr) {

// number relation

}

.

 

 

 

  strs returns [double r]

  { String  a,b; r=0; String str,str1,str2; 

  }

#EQ (a= strs b= strs) {

// strings relation

}

.

 

 

// java ast evaluation 

    CommonAST parseTree = (CommonAST) this.getAST();

    ExpressionTreeWalker walker = new ExpressionTreeWalker();

    String r = walker.expr(parseTree);

 

How is possible to force the relExpression evaluation using the strs.EQ
instead expr.EQ ? ( for example if a code variable indicated this )

 

 

 

I hope to be clear,

 

Thanks a lot!

Bye

Alessandro 

 

 

 

 

 

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