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/* 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/ParseTree.h"
#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 std::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 std::any visitChildren(ParseTree *node) override {
std::any result = defaultResult();
size_t n = node->children.size();
for (size_t i = 0; i < n; i++) {
if (!shouldVisitNextChild(node, result)) {
break;
}
std::any childResult = node->children[i]->accept(this);
result = aggregateResult(std::move(result), std::move(childResult));
}
return result;
}
/// The default implementation returns the result of
/// <seealso cref="#defaultResult defaultResult"/>.
virtual std::any visitTerminal(TerminalNode * /*node*/) override {
return defaultResult();
}
/// The default implementation returns the result of
/// <seealso cref="#defaultResult defaultResult"/>.
virtual std::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 std::any()}.
/// </summary>
/// <returns> The default value returned by visitor methods. </returns>
virtual std::any defaultResult() {
return std::any();
}
/// <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 std::any aggregateResult(std::any /*aggregate*/, std::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 std::any &/*currentResult*/) {
return true;
}
};
} // namespace tree
} // namespace antlr4