Variables

Variables let you write a session once and run it with many different concrete values. They also allow later Behaviors to reference data captured from earlier ones.

Capturing values

Use capture: on any Behavior to name a value you want to save:

- actor: assistant
  action: calls
  target: Order MCP
  capture:
    order_id: "{{response.body.id}}"

The capture key (order_id) becomes available as {{order_id}} for all subsequent Behaviors in the same Session.

Referencing captured values

- actor: assistant
  action: informs
  content: "Your order {{order_id}} is on the way."

Runtime bindings

Values can also be provided at execution time — via dataset row, CLI flag, or environment variable:

abslang run session.abs.yaml --var user_name="Alice"

session: Greeting
behaviors:
  - actor: user
    action: says
    content: "Hi, I'm {{user_name}}"

Resolution order

When resolving {{variable}}, implementations MUST follow this precedence:

1. Captured value — nearest prior capture: of that name in the same Session.
2. Runtime binding — provided at execution time.
3. Error — if no resolution source exists.

Design rationale

Placeholders without runtime bindings are a feature, not a bug. A session with {{user_name}} is a template — it describes the shape of an interaction without committing to concrete values. The same session can be run against a dataset of 100 user names, or with a different value each time via CLI.