org.antlr.v4.runtime.tree.IterativeParseTreeWalker Maven / Gradle / Ivy
/*
* Copyright (c) 2012-2017 The ANTLR Project. All rights reserved.
* Use of this file is governed by the BSD 3-clause license that
* can be found in the LICENSE.txt file in the project root.
*/
package org.antlr.v4.runtime.tree;
import org.antlr.v4.runtime.misc.IntegerStack;
import java.util.ArrayDeque;
import java.util.Deque;
/**
* An iterative (read: non-recursive) pre-order and post-order tree walker that
* doesn't use the thread stack but heap-based stacks. Makes it possible to
* process deeply nested parse trees.
*/
public class IterativeParseTreeWalker extends ParseTreeWalker {
@Override
public void walk(ParseTreeListener listener, ParseTree t) {
final Deque nodeStack = new ArrayDeque();
final IntegerStack indexStack = new IntegerStack();
ParseTree currentNode = t;
int currentIndex = 0;
while (currentNode != null) {
// pre-order visit
if (currentNode instanceof ErrorNode) {
listener.visitErrorNode((ErrorNode) currentNode);
}
else if (currentNode instanceof TerminalNode) {
listener.visitTerminal((TerminalNode) currentNode);
}
else {
final RuleNode r = (RuleNode) currentNode;
enterRule(listener, r);
}
// Move down to first child, if exists
if (currentNode.getChildCount() > 0) {
nodeStack.push(currentNode);
indexStack.push(currentIndex);
currentIndex = 0;
currentNode = currentNode.getChild(0);
continue;
}
// No child nodes, so walk tree
do {
// post-order visit
if (currentNode instanceof RuleNode) {
exitRule(listener, (RuleNode) currentNode);
}
// No parent, so no siblings
if (nodeStack.isEmpty()) {
currentNode = null;
currentIndex = 0;
break;
}
// Move to next sibling if possible
currentNode = nodeStack.peek().getChild(++currentIndex);
if (currentNode != null) {
break;
}
// No next, sibling, so move up
currentNode = nodeStack.pop();
currentIndex = indexStack.pop();
} while (currentNode != null);
}
}
}