Nested flows

Flows can invoke components, but they can also invoke other flows. This allows for flow reuse and organization of complex bots. It is a powerful tool when used effectively.

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Nested flow tip #1

Nested flows are useful for authorization (asking for keys, login, tokens) and retrieving one-time user profile information (email, location, preference, DOB)

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Nested flow tip #2

You can create flows with unlikely keyword triggers like _flow_name_ to create flows that you call from other flows that won't be called directly from the user. You can invoke them by typing _flow_name_ from within the chat.

1. Retrieve information

Note that the first state check_age will invoke another flow and then move forward either to state ask or block based on the return value. (ie. if the user is under 18, they can't order pizza).

states:
    age_check:
        flow: check_age
        transitions:
            allow: ask
            block: fail
    ask:
        component: meya.input_string
        properties:
            output: pizza_type
            text: What type of pizza?
    done:
        component: meya.text
        properties:
            text: "Thanks, we've received your order!"
        return: true
    fail:
        component: meya.pass
        return: true

2. Custom intent + data

In this case, a master flow will invoke a nested flow at an alternative starting point and pass in some data that the flow will use.

states:
    first:
        flow: nested_flow
        intent: alternative
        data:
        	favorite: cat

Note that alternative intent points to the second state.

intents:
    start: first
    alternative: second
states:
    first:
        component: meya.text
        properties:
            text: The first step
        return: true
    second:
        component: meya.text
        properties:
            text: The second step and {{ flow.favorite }} is your favorite.
        return: true

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Not all launched flows are sub-flows

Flows launched from buttons are not considered sub-flows, instead they launch a separate chain of events. Once complete, the flow will not return to the flow that called it.

Flows launched from states are considered sub-flows and will return to the flows from which they were called.

Getting a return value from a child flow

You may need insight into what happened in the child flow. While the child flow could store data in a table which is then retrieved from the parent, return values are another option.

When a child flow ends, the name of the final state that was executed in the child flow becomes the action that is sent back to the parent flow. Recall that actions are used to select transitions. So you can use the child flow's returned action to select which parent state to move to next.

Example

Try creating these two flows:

states:
    first:
        component: meya.text
        properties:
            text: "parent flow; first state"

    launch:
        flow: child
        transitions:
            yes_state: second
            no_state: third

    second:
        component: meya.text
        properties:
            text: "parent flow; second state"
        return: true

    third:
        component: meya.text
        properties:
            text: "parent flow; third state"
        return: true

states:
    first:
        component: meya.text
        properties:
            text: "child flow; first state"
    
    yes_no_state:
        component: meya.nlp_yes_no
        properties:
            text: "Yes or no?"
        transitions:
            'yes': yes_state
            'no': no_state

    yes_state:
        component: meya.text
        properties:
            text: "child flow; yes state"
        return: true
        
    no_state:
        component: meya.text
        properties:
            text: "child flow; no state"
        return: true

Start the parent flow and answer yes.

Because you entered yes, the child flow executed the yes_state. The value yes_state was then returned to the parent flow as an action, which then selected the second state to execute next.

Restart the parent flow and answer no.

This time, no_state was the returned action, and so the third state in the parent flow was executed.