add antlr

lib/antlr4/include/tree/AbstractParseTreeVisitor.h

@@ -0,0 +1,128 @@
+/* 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 "tree/ParseTreeVisitor.h"
+
+namespace antlr4 {
+namespace tree {
+
+  class ANTLR4CPP_PUBLIC AbstractParseTreeVisitor : public ParseTreeVisitor {
+  public:
+    /// The default implementation calls <seealso cref="ParseTree#accept"/> on the
+    /// specified tree.
+    virtual antlrcpp::Any visit(ParseTree *tree) override {
+      return tree->accept(this);
+    }
+
+    /**
+     * <p>The default implementation initializes the aggregate result to
+     * {@link #defaultResult defaultResult()}. Before visiting each child, it
+     * calls {@link #shouldVisitNextChild shouldVisitNextChild}; if the result
+     * is {@code false} no more children are visited and the current aggregate
+     * result is returned. After visiting a child, the aggregate result is
+     * updated by calling {@link #aggregateResult aggregateResult} with the
+     * previous aggregate result and the result of visiting the child.</p>
+     *
+     * <p>The default implementation is not safe for use in visitors that modify
+     * the tree structure. Visitors that modify the tree should override this
+     * method to behave properly in respect to the specific algorithm in use.</p>
+     */
+    virtual antlrcpp::Any visitChildren(ParseTree *node) override {
+      antlrcpp::Any result = defaultResult();
+      size_t n = node->children.size();
+      for (size_t i = 0; i < n; i++) {
+        if (!shouldVisitNextChild(node, result)) {
+          break;
+        }
+
+        antlrcpp::Any childResult = node->children[i]->accept(this);
+        result = aggregateResult(result, childResult);
+      }
+
+      return result;
+    }
+
+    /// The default implementation returns the result of
+    /// <seealso cref="#defaultResult defaultResult"/>.
+    virtual antlrcpp::Any visitTerminal(TerminalNode * /*node*/) override {
+      return defaultResult();
+    }
+
+    /// The default implementation returns the result of
+    /// <seealso cref="#defaultResult defaultResult"/>.
+    virtual antlrcpp::Any visitErrorNode(ErrorNode * /*node*/) override {
+      return defaultResult();
+    }
+
+  protected:
+    /// <summary>
+    /// Gets the default value returned by visitor methods. This value is
+    /// returned by the default implementations of
+    /// <seealso cref="#visitTerminal visitTerminal"/>, <seealso cref="#visitErrorNode visitErrorNode"/>.
+    /// The default implementation of <seealso cref="#visitChildren visitChildren"/>
+    /// initializes its aggregate result to this value.
+    /// <p/>
+    /// The base implementation returns {@code null}.
+    /// </summary>
+    /// <returns> The default value returned by visitor methods. </returns>
+    virtual antlrcpp::Any defaultResult() {
+      return nullptr; // support isNotNull
+    }
+
+    /// <summary>
+    /// Aggregates the results of visiting multiple children of a node. After
+    /// either all children are visited or <seealso cref="#shouldVisitNextChild"/> returns
+    /// {@code false}, the aggregate value is returned as the result of
+    /// <seealso cref="#visitChildren"/>.
+    /// <p/>
+    /// The default implementation returns {@code nextResult}, meaning
+    /// <seealso cref="#visitChildren"/> will return the result of the last child visited
+    /// (or return the initial value if the node has no children).
+    /// </summary>
+    /// <param name="aggregate"> The previous aggregate value. In the default
+    /// implementation, the aggregate value is initialized to
+    /// <seealso cref="#defaultResult"/>, which is passed as the {@code aggregate} argument
+    /// to this method after the first child node is visited. </param>
+    /// <param name="nextResult"> The result of the immediately preceeding call to visit
+    /// a child node.
+    /// </param>
+    /// <returns> The updated aggregate result. </returns>
+    virtual antlrcpp::Any aggregateResult(antlrcpp::Any /*aggregate*/, const antlrcpp::Any &nextResult) {
+      return nextResult;
+    }
+
+    /// <summary>
+    /// This method is called after visiting each child in
+    /// <seealso cref="#visitChildren"/>. This method is first called before the first
+    /// child is visited; at that point {@code currentResult} will be the initial
+    /// value (in the default implementation, the initial value is returned by a
+    /// call to <seealso cref="#defaultResult"/>. This method is not called after the last
+    /// child is visited.
+    /// <p/>
+    /// The default implementation always returns {@code true}, indicating that
+    /// {@code visitChildren} should only return after all children are visited.
+    /// One reason to override this method is to provide a "short circuit"
+    /// evaluation option for situations where the result of visiting a single
+    /// child has the potential to determine the result of the visit operation as
+    /// a whole.
+    /// </summary>
+    /// <param name="node"> The <seealso cref="ParseTree"/> whose children are currently being
+    /// visited. </param>
+    /// <param name="currentResult"> The current aggregate result of the children visited
+    /// to the current point.
+    /// </param>
+    /// <returns> {@code true} to continue visiting children. Otherwise return
+    /// {@code false} to stop visiting children and immediately return the
+    /// current aggregate result from <seealso cref="#visitChildren"/>. </returns>
+    virtual bool shouldVisitNextChild(ParseTree * /*node*/, const antlrcpp::Any &/*currentResult*/) {
+      return true;
+    }
+
+  };
+
+} // namespace tree
+} // namespace antlr4