new_contents: # -*- coding: utf-8 -*-
  
  # Copyright (c) 2017 Ericsson AB
  #
  # 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.
  
  from calvin.actor.actor import Actor, manage, condition, stateguard, calvinsys
  
  class HallEffect(Actor):
      """
      React to presence of magnetic field.
  
      Output:
        state : true if magnetic field present, false otherwise
      """
  
      @manage(include=[])
      def init(self):
          self.setup()
  
      def setup(self):
          self.sensor = calvinsys.open(self, "calvinsys.io.hallswitch")
  
      def will_migrate(self):
          calvinsys.close(self.sensor)
          self.sensor = None
  
      def will_end(self):
          if self.sensor:
              calvinsys.close(self.sensor)
  
      def did_migrate(self):
          self.setup()
  
      @stateguard(lambda self: calvinsys.can_read(self.sensor))
      @condition([], ["state"])
      def state_change(self):
          value = calvinsys.read(self.sensor)
          return (True if value else False,)
  
      action_priority = (state_change, )
      requires = ['calvinsys.io.hallswitch']
  
subject: Add HallEffect Sensor