Finite State Machine

The Finite State Machine (FSM) is based on the one shown in this article. The states, commands, default messages and transitions are described in the fsm.yml file:

transitions:
  - from:
      - "off"
    into: "on"
    command: "turn_on"
    answers:
      - text: "Turning on."

  - from:
      - "on"
    into: "off"
    command: "turn_off"
    answers:
      - text: "Turning off."
      - text: "❌"

defaults:
  unknown: "Can't do that."

Under transitions you can list the transitions available for the FSM. Each object describes the states of the transition (from a list of states into another state) if command is executed; answers is the list of messages to send to the user.

In other words:

  - from:
      - "off"                # the list of origin states
    into: "on"               # the target state
    command: "turn_on"       # the command that will do the transition
    answers:
      - text: "Turning on."  # the answers that are sent after the transition

The commands used in the transitions must correspond with the ones listed in the classifier.

Answers

Answers are formed by a text field and/or an image URL. For example:

    answers:
      - text: "Single message."

    answers:
      - text: "A list"
      - text: "of simple messages"

    answers:
      - text: "An image will be attached"
      - text: "to this message"
        image: https://i.imgur.com/8MU0IUT.jpeg

Any

The special state any can help you go from any state into another, if the command is executed.

  # The "end" command will move from any state into the
  # initial state, sending the message "Bye bye!"
  - from:
      - any
    into: initial
    command: end
    answers:
      - text: "Bye bye!"

Also, the special command any is used to transition between states, regardless of the command predicted.

  # When in the "search_pokemon" state, any command will do the
  # transition into the initial state
  - from:
      - search_pokemon
    into: initial
    command: any
    extension:
      server: pokemon
      name: search_pokemon

Default Messages

In the fsm.yml file, the defaults section is used to set the messages that will be returned when the following events happen:

• unknown: The current state does not transition into another one with the predicted command.
• unsure: The command prediction confidence was below the threshold.
• error: An error ocurred during the execution of an extension.

Here's an example of default messages:

defaults:
  unknown: "Can't do that transition."
  unsure: "Sorry, I didn't understand that."
  error: "An error ocurred."

Slots

You can save information from the user's input by using slot objects. In the fsm.yml file, slots are declared as such:

  - from:
      - question_1
    into: question_2
    command: any
    extension:
      server: trivia
      name: val_ans_1
    slot:
      name: answer_1
      mode: whole_text

In this example, in the transition from question_1 to question_2, a slot called answer_1 will be saved, in other words, the user's message is stored in memory.

The supported slot modes are:

• whole_text: Saves the entire input in the slot.

  slot:
    name: answer_1
    mode: whole_text
  

• regex: Saves the first Regular Expression match found.

  slot:
    name: answer_1
    mode: regex
    regex: "[0-9]+"