ludic/docs/language/control/kw-become.md

id	name	category	kind	tokens	sig	tip	order
kw-become	become	control	keyword	become	become Name	Transition to another state of the enclosing machine, or to another scene.	8

A become statement performs a transition. Inside a machine, become Name moves to another state of that machine by storing the target state's value back into the machine's store, so the next dispatch runs the new state. Used from a scene's layer handler, become Scene instead switches the active scene: the current scene's on exit runs, the active-scene register is set, and the target scene's on enter runs — two direct calls and a store, with no dispatch table. become names its target and knows from context which kind of transition it is, so you rarely think about the machinery. Transitioning is cheap and takes effect immediately for machine states.

program EncounterFlow {
  enum Stage { Explore, Battle, Victory }
  var stage: int = Stage.Explore
  var enemies_left: int = 2

  handler RunStage phase Update {
    machine stage {
      state Explore {
        if Input.key() == ' ' { become Battle }
      }
      state Battle {
        if enemies_left <= 0 { become Victory }
      }
      state Victory {
        Screen.status("you win")
      }
    }
  }
}