ParseTree traversal in antlr4 Code Answer

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I am using antlr4 c++. I have a ParseTree and I am trying to recreate the tree structure. To to this I am using a Visitor my_Visitor and my own node object(s).

My problem is that visitChildren(tree::RuleNode*) calls the visit functions of all children, so I am losing the information when one child tree is traversed and the next child tree is visited.

Assume a tree like this:

  A
 / 
B   C

When I call visitChildren(A) (using overloaded visitExpression(ExpressionContext*) functions for B and C), I can extract the information that the visit sequence is A,B,C.

This sequence could also result from:

A
|
B
|
C

To recreate the tree I think I would need something like

antlrcpp::Any my_Visitor::my_visitChildren(tree::RuleNode* A){
    for(int i=0;i<A->children.size();i++){
        //create a new node in my own tree representation as child of A
        visit(A->children[i]);
    }
}

and call my_visitChildren in my overloaded visitExpression functions.

The problem here is that A->children[i] is a Tree and visit(.) needs a ParseTree.

Can I somehow create a ParseTree from children[i] or is there a better approach to do this?

I am also thinking about using a map from tree->parent to my objects and just attach my new node there, but this is not optimal if I wanted to omit some nodes (e.g. for an AST).

Answer

The differentiation between a ParseTree and a Tree is purely artificial and in fact of no real use. The children of a tree node are in fact all ParseTree instances. There are a few tree classes that are never used in the runtime, except for building the base classes of ParseTree. Hence later on I have removed Tree, SyntaxTree and RuleNode and put all that together into the ParseTree class.

To answer your question: you can safely cast the child nodes to ParseTree for your tree walk.

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