Back Operator
-------------


In this example, when the ``>back`` operator is triggered by ``Port3In`` in the
state `WaitForExit`, the state machine returns to the state that previously
transitioned into `WaitForExit` - either `FlashPort1` or `FlashPort2`.

.. image:: back_operator.svg
   :align: center

.. tab-set::

   .. tab-item:: Python

    .. literalinclude:: ../../../../examples/back_operator.py
       :language: python
       :start-at: from bpod_core.

   .. tab-item:: JSON

    .. code-block:: json

       {
         "states": {
           "WaitForChoice": {
             "transitions": {
               "Port1_High": "FlashPort1",
               "Port2_High": "FlashPort2"
             }
           },
           "FlashPort1": {
             "timer": 0.5,
             "transitions": {
               "Tup": "WaitForExit"
             },
             "actions": {
               "PWM1": 255
             }
           },
           "FlashPort2": {
             "timer": 0.5,
             "transitions": {
               "Tup": "WaitForExit"
             },
             "actions": {
               "PWM2": 255
             }
           },
           "WaitForExit": {
             "transitions": {
               "Port1_High": ">exit",
               "Port2_High": ">exit",
               "Port3_High": ">back"
             }
           }
         }
       }

   .. tab-item:: YAML

    .. code-block:: yaml

       states:
         WaitForChoice:
           transitions:
             Port1_High: FlashPort1
             Port2_High: FlashPort2
         FlashPort1:
           timer: 0.5
           transitions:
             Tup: WaitForExit
           actions:
             PWM1: 255
         FlashPort2:
           timer: 0.5
           transitions:
             Tup: WaitForExit
           actions:
             PWM2: 255
         WaitForExit:
           transitions:
             Port1_High: '>exit'
             Port2_High: '>exit'
             Port3_High: '>back'