text: ////////////////////////////////////////////////////////////////////////////////
  /// DISCLAIMER
  ///
  /// Copyright 2014-2021 ArangoDB GmbH, Cologne, Germany
  /// Copyright 2004-2014 triAGENS GmbH, Cologne, Germany
  ///
  /// Licensed under the Apache License, Version 2.0 (the "License");
  /// you may not use this file except in compliance with the License.
  /// You may obtain a copy of the License at
  ///
  ///     http://www.apache.org/licenses/LICENSE-2.0
  ///
  /// Unless required by applicable law or agreed to in writing, software
  /// distributed under the License is distributed on an "AS IS" BASIS,
  /// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  /// See the License for the specific language governing permissions and
  /// limitations under the License.
  ///
  /// Copyright holder is ArangoDB GmbH, Cologne, Germany
  ///
  /// @author Michael Hackstein
  ////////////////////////////////////////////////////////////////////////////////
  
  #ifndef ARANGOD_AQL_EXECUTION_STATE_H
  #define ARANGOD_AQL_EXECUTION_STATE_H 1
  
  #include <iosfwd>
  
  namespace arangodb {
  namespace aql {
  
  enum class ExecutionState {
    // done with this block, definitely no more results
    DONE,
    // (potentially) more results available. this may "lie" and
    // report that there are more results when in fact there are
    // none (background: to accurately determine that there are
    // more results we may need to execute expensive operations
    // on the preceeding blocks, which we want to avoid)
    HASMORE,
    // unclear if more results available or not. caller is asked
    // to try again
    WAITING
  };
  
  enum class ExecutorState {
    // done with this block, definitely no more results
    DONE,
    // (potentially) more results available. this may "lie" and
    // report that there are more results when in fact there are
    // none (background: to accurately determine that there are
    // more results we may need to execute expensive operations
    // on the preceeding blocks, which we want to avoid)
    HASMORE
  };
  
  std::ostream& operator<<(std::ostream& ostream, ExecutionState state);
  
  std::ostream& operator<<(std::ostream& ostream, ExecutorState state);
  
  }  // namespace aql
  }  // namespace arangodb
  #endif
  