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Conditions in Flows

Conditions​

Conditions are used in flows in three different places:

  • In flow guards to determine whether a flow can be started.
  • In the next field of a flow step to choose between branches of your business logic.
  • In the rejections field of a collect step to validate slot values.

Syntax​

Conditions in flows are written using natural language that can include logical operators, conditional operators and other constructs. They are evaluated with the pypred library.

These conditions support the following operators,

  • not: Negates a condition.
  • and: Combines two conditions with logical AND.
  • or: Combines two conditions with logical OR.
  • >: Greater than.
  • >=: Greater than or equal to.
  • <: Less than.
  • <=: Less than or equal to.
  • =: Equal to.
  • !=: Not equal to.
  • is: Checks for identity.
  • is not: Checks for non-identity.
  • contains: Subset operator that checks if a set contains a value
  • matches: Uses regular expressions to match strings.

Parentheses​

Use parentheses to group expressions and control the order of evaluation. For example:

- collect: age
  next:
    - if: slots.age < 18
      then: under_18_step
    - if: (slots.age > 18 and (consent = "yes" or consent = "y"))
      then: consent_accept
    - else: consent_decline

Subset Operator​

Subset operator contains can be used in the format SET contains VALUE where SET is the set of possible values and VALUE being the name of slot. For example:

- collect: emergency
  next:
    - if: "{'WARN' 'ERR' 'CRIT'} contains slots.error_level"
      then: handoff
    - else: everything_okay

contains operator can also be used to identify substrings when used as slots.product contains "Rasa" however this check is case-sensitive.

Constants​

  • String literals: Enclose in single or double quotes ('example' or "example").
  • Numeric literals: Numbers without quotes (42).
  • Constants: true, false, undefined, null, empty

Regular Expressions​

When using the matches operator, you can include regular expression modifiers. The regex modifier should be enclosed in quotes. For example, this flow step checks if the zipcode slot contains a United States zip code :

- collect: zipcode
  description: ask zipcode and check if its a zip code
  next:
    - if: slots.zipcode matches "\d{5}(-\d{4})?"
      then: ask_payment
    - else: wrong_zipcode

A case-insensitive substring comparison can be made with the condition product matches "(?i).*rasa.*" which checks for the substring rasa within the variable product.

Empty Values​

If you want to check if a boolean slot is not set, you need to use the syntax <boolean-slot> is null.

To check if a text slot is not set or empty, use the syntax not <text-slot>.

Examples​

Here are some examples of conditions that demonstrate the use of different constructs.

# Simple conditions
age > 18
name is "Alice"
name is empty
status = "active"
status is not null

# Combining Conditions
age > 21 and gender = "female"
category = "electronics" or category = "computers"
status = "active" and (priority = 1 or priority = 2)
status = empty or status is null
description matches "/error \d{3}/i" and (severity = "high" or source contains "server")

Namespaces​

Namespaces are used to access different types of data in predicates used in branching conditions, slot validation, and flow guards. There are two available namespaces: slots and context. The slots namespace is used to access slot values, while the context namespace is used to access the current dialogue frame properties.

Slots​

The slots namespace is used to access slot values. The slot name must be prefixed with slots. to be accessible in the condition. For example:

- id: some_question
  collect: age
  next:
    - if: slots.age < 18
      then: under_18_step
    - else: over_18_step

Make sure to have the slot defined in the domain. If the slot is not defined in the domain or the slot is not prefixed with slots. namespace, the validation that runs during training will fail with an appropriate error.

Context​

The context namespace is used to access the properties of the current dialogue frame. The property must be prefixed with context. to be accessible in the predicate. For example:

  pattern_completed:
    description:  a flow has been completed and there is nothing else to be done
    steps:
      - noop: true
        next:
          - if: context.previous_flow_name != "greeting"
            then:
              - action: utter_what_can_help_with
                next: END
          - else: stop
      - id: stop
        action: action_stop

You can also use jinja templating to access the context namespace. For example:

  pattern_completed:
    description:  a flow has been completed and there is nothing else to be done
    steps:
      - noop: true
        next:
          - if: "{{context.previous_flow_name}}" != "greeting"
            then:
              - action: utter_what_can_help_with
                next: END
          - else: stop
      - id: stop
        action: action_stop

Dialogue Frames​

The dialogue manager organizes the advancement of flows (both user defined and built-in) in a dialogue frame stack. The dialogue frame stack represents a LIFO (Last-In-First-Out) stack of dialogue frames. Different types of dialogue frames are mapped to built-in conversational patterns that enable conversation repair.

Each dialogue frame has a flow_id and step_id property. The flow_id is the id of the current flow and the step_id is the id of the current step in the flow.

The following dialogue frames types are available:

  1. cancel: handles flow cancellation
  2. chitchat: handles chitchat
  3. clarify: handles clarification
  4. collect information: handles information collection
  5. completion: handles flow completion
  6. continue interrupted: handles continuation of interrupted flows
  7. correction: handles correction
  8. internal error: handles internal errors
  9. search: handles knowledge search
  10. skip question: handles skipping of information collection
  11. code change: cleans the stack after an assistant update
  12. can not handle: handles situations where the assistant cannot handle
  13. human handoff: handles handoff to human
  14. validate slot: handles real-time slot validations that are strictly independent of business logic
Cancel​

The flow_id is pattern_cancel_flow. The step_id is START. In addition, the following properties are available:

  • canceled_name: the name of the flow that should be canceled
  • canceled_frames: the list of stack frames that should be canceled
Chitchat​

The flow_id is pattern_chitchat. The step_id is START.

Clarify​

The flow_id is pattern_clarify. The step_id is START. In addition, the following properties are available:

  • names: the list of names of the flows that the user can choose from
  • clarification_options: the options that the user can choose from as a string
Collect Information​

The flow_id is pattern_collect_information. The step_id is START. In addition, the following properties are available:

  • collect: the name of the slot that should be filled
  • utter: the response that should be executed to ask the user for information
  • collect_action: the action that should be executed to ask the user for information
  • rejections: the optional list of validation checks that should be executed if the user provides invalid information

Note that if you are using the context.collect property in your flow, you must write this in jinja templating style and prefix it with the slots. namespace. This is because context.collect corresponds to the slot name, and every slot must be preceded by the slots. namespace.

For example:

  pattern_collect_information:
    name: "pattern_collect_information"
    description:  the assistant is collecting information from the user
    steps:
      - id: check
        next:
          - if: "slots.{{context.collect}} is not null"
            then:
              - action: utter_ask_age
                next: listen
          - else: END
      - id: listen
        action: action_listen
Completion​

The flow_id is pattern_completed. The step_id is START. In addition, the following properties are available:

  • previous_flow_name: the name of the flow that has been completed
Continue Interrupted​

The flow_id is pattern_continue_interrupted. The step_id is START. In addition, the following properties are available:

  • previous_flow_name: the name of the flow that was interrupted
  • interrupted_flow_names: names of the previous flows that were interrupted
  • interrupted_flow_ids: ids of the previous flows that were interrupted
  • interrupted_flow_options: options of interrupted flows that the user can choose from as a string
  • multiple_flows_interrupted: boolean indicating whether multiple flows were interrupted
Correction​

The flow_id is pattern_correction. The step_id is START. In addition, the following properties are available:

  • is_reset_only: indicates if the correction is only a reset of the flow
  • corrected_slots: slot key-value pairs that should be corrected
  • reset_flow_id: the ID of the flow to reset to, defaults to None
  • reset_step_id: the ID of the step to reset to, defaults to None
Internal Error​

The flow_id is pattern_internal_error. The step_id is START. In addition, the following properties are available:

  • error_type: string indicates the type of error
  • info: additional info to be provided to the user

The flow_id is pattern_search. The step_id is START.

Skip Question​

The flow_id is pattern_skip_question. The step_id is START.

Code Change​

The flow_id is pattern_code_change. The step_id is START.

Can Not Handle​

The flow_id is pattern_cannot_handle. The step_id is START. In addition, the following properties are available:

  • reason: string indicates the reason why the assistant cannot handle
Human Handoff​

The flow_id is pattern_human_handoff. The step_id is START.

Validate Slot​
New in 3.12

You can now enable real-time slot validation in Rasa Pro 3.12.0.

The flow_id is pattern_validate_slot. The step_id is START. In addition, the following properties are available:

  • validate: the name of the slot that should be validated
  • refill_utter: the response that should be executed to ask the user to refill the invalid slot
  • refill_action: the action that should be executed to ask the user to refill the invalid slot
  • rejections: the list of validation checks that should be executed if the user provides information for a slot that requires validation

Note that if you are using the context.validate property in your flow, you must write this in jinja templating style and prefix it with the slots. namespace. This is because context.validate corresponds to the slot name, and every slot must be preceded by the slots. namespace.

For example:

  pattern_validate_slot:
    name: "pattern_validate_slot"
    description:  the assistant is validating information received from the user
    steps:
      - id: check
        next:
          - if: "slots.{{context.validate}} is not null"
            then:
              - action: utter_refill_age
                next: listen
          - else: END
      - id: listen
        action: action_listen
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