JavaCC dump method to print AST

问题:

I am using JavaCC to print an AST in a particular format. I need it to be like this :

LetNode( Identier(X), ExprNode( PlusNode( IntegerLiteral(8), IntegerLiteral(2) ))) 

but I am getting:

Start(LetNode(Identifier(x)(ExprNode(IntegerLiteral(5)(PlusNode(IntegerLiteral(5)()))

I am using the dump method to print this:

public void dump(String prefix) {
  System.out.print(toString(prefix));
  System.out.print("(");
  if (children != null) {

    for (int i = 0; i < children.length; ++i) {
      SimpleNode n = (SimpleNode)children[i];
      if (n != null) {
        n.dump(prefix +"");
      }
    }
    System.out.print(")");
  }
}

}

The output without any modification is :

Start
  Sxl
   Statement
    VariableDecl
     Identifier
     Type
     Expression
      SimpleExpression
       Term
        Factor
         Literal
          IntegerLiteral
       AdditiveOp
       Term
        Factor
         Literal
          IntegerLiteral

My method:

void AdditiveOp():
{}  
{
   (Plus() /*#Add(2)*/ | Minus() | Or())

}

void Plus():
{
}
{
  (< PLUS >)
  #PlusNode
}

If I remove the /* */ it does not work as it says it expects something else not +

Any help would be greatly appreciated!

回答1:

The usual way to make an AST with JJT for an expression grammar is to do something like this

void AdditiveExpression() #void :
{ Token t ; }
{
  MultiplicativeExpression()
  (  "+"  MultiplicativeExpression()  #Add(2)
  |  "-"  MultiplicativeExpression()  #Subtract(2)   
  )*
}