Add an iterative version of the ParseTreeWalker

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

@@ -0,0 +1,151 @@
+/*
+ * [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;
+
+/**
+ * An iterative (read: non-recursive) pre-order and post-order tree walker that
+ * doesn't use the thread stack but it's own heap-based stack using linked data
+ * structures. Makes it possible to process deeply nested parse trees.
+ */
+public class IterativeParseTreeWalker extends ParseTreeWalker {
+    public static final ParseTreeWalker DEFAULT = new IterativeParseTreeWalker();
+
+    @Override
+    public void walk(final ParseTreeListener listener, final ParseTree t) {
+        for (WalkerNode<?> currentNode = createNode(null, t, 0); currentNode != null;) {
+            currentNode.enter(listener); // Pre order visit
+
+            // Move down to first child
+            WalkerNode<?> nextNode = currentNode.getFirstChild();
+            if (nextNode != null) {
+                currentNode = nextNode;
+                continue;
+            }
+
+            // No child nodes, so walk tree
+            while (currentNode != null) {
+                currentNode.exit(listener); // Post order visit
+
+                // Move to sibling if possible
+                nextNode = currentNode.getNextSibling();
+                if (nextNode != null) {
+                    currentNode = nextNode;
+                    break;
+                }
+
+                // Move up
+                currentNode = currentNode.getParentNode();
+            }
+        }
+    }
+
+    protected WalkerNode<?> createNode(final WalkerNode<?> parent, final ParseTree self, final int pos) {
+        if (self instanceof ErrorNode) {
+            return new ErrorWalkerNode(parent, (ErrorNode) self, pos);
+        } else if (self instanceof TerminalNode) {
+            return new TerminalWalkerNode(parent, (TerminalNode) self, pos);
+        } else {
+            return new RuleWalkerNode(parent, (RuleNode) self, pos);
+        }
+    }
+
+    protected abstract class WalkerNode<N extends ParseTree> {
+        private final WalkerNode<?> parent;
+        protected final N self;
+        private final int pos;
+
+        protected WalkerNode(final WalkerNode<?> parent, final N self, final int pos) {
+            this.parent = parent;
+            this.self = self;
+            this.pos = pos;
+        }
+
+        public WalkerNode<?> getFirstChild() {
+            return self.getChildCount() > 0 ? createChildNode(0) : null;
+        }
+
+        public WalkerNode<?> getNextSibling() {
+            return parent != null && parent.self.getChildCount() > pos + 1 ? parent.createChildNode(pos + 1) : null;
+        }
+
+        public WalkerNode<?> getParentNode() {
+            return parent;
+        }
+
+        public abstract void enter(ParseTreeListener listener);
+
+        public void exit(final ParseTreeListener listener) {
+            // defaults to do nothing
+        }
+
+        protected WalkerNode<?> createChildNode(final int pos) {
+            return createNode(this, self.getChild(pos), pos);
+        }
+    }
+
+    protected class RuleWalkerNode extends WalkerNode<RuleNode> {
+        public RuleWalkerNode(final WalkerNode<?> parent, final RuleNode self, final int pos) {
+            super(parent, self, pos);
+        }
+
+        @Override
+        public void enter(final ParseTreeListener listener) {
+            enterRule(listener, self);
+        }
+
+        @Override
+        public void exit(final ParseTreeListener listener) {
+            exitRule(listener, self);
+        }
+    }
+
+    protected class ErrorWalkerNode extends WalkerNode<ErrorNode> {
+        public ErrorWalkerNode(final WalkerNode<?> parent, final ErrorNode self, final int pos) {
+            super(parent, self, pos);
+        }
+
+        @Override
+        public void enter(final ParseTreeListener listener) {
+            listener.visitErrorNode(self);
+        }
+    }
+
+    protected class TerminalWalkerNode extends WalkerNode<TerminalNode> {
+        public TerminalWalkerNode(final WalkerNode<?> parent, final TerminalNode self, final int pos) {
+            super(parent, self, pos);
+        }
+
+        @Override
+        public void enter(final ParseTreeListener listener) {
+            listener.visitTerminal(self);
+        }
+    }
+}