//===--- ASTWalker.h - Class for walking the AST ----------------*- C++ -*-===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2015 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See http://swift.org/LICENSE.txt for license information
// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//

#ifndef SWIFT_AST_ASTWALKER_H
#define SWIFT_AST_ASTWALKER_H

#include "llvm/ADT/PointerUnion.h"

namespace swift {

class Decl;
class Expr;
class Stmt;
  
/// \brief An abstract class used to traverse an AST.
class ASTWalker {
public:
  /// \brief The parent of the node we are visiting.
  llvm::PointerUnion<Expr *, Stmt *> Parent;

  /// This method is called when first visiting an expression,
  /// before walking into its children.  If it returns false, the
  /// subtree is ignored.
  ///
  /// The default implementation always returns true.
  virtual bool walkToExprPre(Expr *E) { return true; }

  /// This method is called after visiting an expression's children.
  /// If it returns null, the walk is terminated; otherwise, the
  /// returned expression is spliced in where the old expression
  /// previously appeared.
  ///
  /// The default implementation always returns its argument.
  virtual Expr *walkToExprPost(Expr *E) { return E; }

  /// This method is called when first visiting a statement, before
  /// walking into its children.  If it returns false, the subtree is
  /// ignored.
  ///
  /// The default implementation always returns true.
  virtual bool walkToStmtPre(Stmt *S) { return true; }

  /// This method is called after visiting a statement's children.  If
  /// it returns null, the walk is terminated; otherwise, the returned
  /// statement is spliced in where the old statement previously
  /// appeared.
  ///
  /// The default implementation always returns its argument.
  virtual Stmt *walkToStmtPost(Stmt *S) { return S; }

  
  /// walkToDeclPre - This method is called when first visiting a decl, before
  /// walking into its children.  If it returns false, the subtree is skipped.
  virtual bool walkToDeclPre(Decl *D) { return true; }

  /// walkToDeclPost - This method is called after visiting the children of a
  /// decl.  If it returns false, the remaining traversal is terminated and
  /// returns failure.
  virtual bool walkToDeclPost(Decl *D) { return true; }

protected:
  ASTWalker() = default;
  ASTWalker(const ASTWalker &) = default;
  virtual ~ASTWalker() {}
  
  virtual void anchor();
};

} // end namespace swift

#endif