Reputation: 3
I've been playing around with ANTLR4, trying to convert an ANTLR3 project.
I have generated a lexer, a parser and a visitor class from an ANLTR4 grammar coming from the official repository. In the visitor, I am calling one of my classes using the ctx available from the visitor:
myFunction(ctx.getChild(0))
Then, in myFunction, I want to retrieve the first child having a specific type, so I tried doing:
final ParseTree classNameElement =
(ParseTree) ((GrammarAST) node).getFirstChildWithType(MyParser.IDENTIFIER);
where node is the argument of myFunction, thus a ParseTree. getFirstChildWithType seems to be available only in GrammarAST, hence the cast.
I am getting the error: cannot be cast to org.antlr.v4.tool.ast.GrammarAST
So maybe this is not possible as is and I must have missed something, but I want to find the first child having a specific type from a ParseTree.
Thank you!
Upvotes: 0
Views: 703
Reputation: 6001
Notice that GrammarAST
is in the ANTLR tool
hierarchy. With a generated parse-tree, you should be dealing exclusively with the runtime.
To search a parse-tree node for a child of a given type:
public ParseTree getFirstChildOfType(ParseTree node, int tokentype) {
for (int idx = 0; idx < node.getChildCount(); idx++) {
ParseTree child = node.getChild(idx);
if (child instanceof TerminalNode) {
Token token = (Token) child.getPayload();
if (token.getType() == tokentype) {
return child;
}
}
}
return null;
}
This will get the first direct, i.e., child terminal, of the given type. Will need to recurse into non-TerminalNodes if the absolute first of type is desired.
If the latter is actually the desired function, there may be a better/more direct use of parse-tree walker to obtain the desired overall goal.
Upvotes: 1