Add an iterative version of the ParseTreeWalker

contributors.txt

@@ -94,6 +94,7 @@ YYYY/MM/DD, github id, Full name, email
 2016/03/27, beardlybread, Bradley Steinbacher, bradley.j.steinbacher@gmail.com
 2016/03/29, msteiger, Martin Steiger, antlr@martin-steiger.de
 2016/03/28, gagern, Martin von Gagern, gagern@ma.tum.de
+2016/07/10, twz123, Tom Wieczorek, tom.wieczorek@zalando.de
 2016/07/20, chrisheller, Chris Heller, chris.heller.greyheller@gmail.com
 2016/07/20, nburles, Nathan Burles, nburles@gmail.com
 2016/07/20, kosl90, Li Liqiang, kos1990l@gmail.com

runtime/Java/src/org/antlr/v4/runtime/tree/IterativeParseTreeWalker.java

@@ -0,0 +1,103 @@
+/*
+ * [The "BSD license"]
+ *  Copyright (c) 2012 Terence Parr
+ *  Copyright (c) 2012 Sam Harwell
+ *  All rights reserved.
+ *
+ *  Redistribution and use in source and binary forms, with or without
+ *  modification, are permitted provided that the following conditions
+ *  are met:
+ *
+ *  1. Redistributions of source code must retain the above copyright
+ *     notice, this list of conditions and the following disclaimer.
+ *  2. Redistributions in binary form must reproduce the above copyright
+ *     notice, this list of conditions and the following disclaimer in the
+ *     documentation and/or other materials provided with the distribution.
+ *  3. The name of the author may not be used to endorse or promote products
+ *     derived from this software without specific prior written permission.
+ *
+ *  THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+ *  IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ *  OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ *  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+ *  INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ *  NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ *  DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ *  THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ *  (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ *  THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package org.antlr.v4.runtime.tree;
+
+import java.util.ArrayDeque;
+import java.util.Deque;
+
+import org.antlr.v4.runtime.misc.IntegerStack;
+
+/**
+ * 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<ParseTree> nodeStack = new ArrayDeque<ParseTree>();
+		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);
+		}
+	}
+}

runtime/Java/src/org/antlr/v4/runtime/tree/ParseTreeWalker.java

@@ -34,7 +34,7 @@
 import org.antlr.v4.runtime.RuleContext;
 
 public class ParseTreeWalker {
-    public static final ParseTreeWalker DEFAULT = new ParseTreeWalker();
+    public static final ParseTreeWalker DEFAULT = new IterativeParseTreeWalker();
 
     public void walk(ParseTreeListener listener, ParseTree t) {
 		if ( t instanceof ErrorNode) {