add antlr

lib/antlr4/include/tree/ParseTreeWalker.h

@@ -0,0 +1,31 @@
+/* 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.
+ */
+
+#pragma once
+
+#include "antlr4-common.h"
+
+namespace antlr4 {
+namespace tree {
+
+  class ANTLR4CPP_PUBLIC ParseTreeWalker {
+  public:
+    static ParseTreeWalker &DEFAULT;
+
+    virtual ~ParseTreeWalker();
+
+    virtual void walk(ParseTreeListener *listener, ParseTree *t) const;
+
+  protected:
+    /// The discovery of a rule node, involves sending two events: the generic
+    /// <seealso cref="ParseTreeListener#enterEveryRule"/> and a
+    /// <seealso cref="RuleContext"/>-specific event. First we trigger the generic and then
+    /// the rule specific. We do them in reverse order upon finishing the node.
+    virtual void enterRule(ParseTreeListener *listener, ParseTree *r) const;
+    virtual void exitRule(ParseTreeListener *listener, ParseTree *r) const;
+  };
+
+} // namespace tree
+} // namespace antlr4