ludic/docs/language/events/kw-emit.md

---

id: kw-emit name: emit category: events kind: keyword tokens: emit sig: emit Name(field: value) tip: Fire an event, running every listener; as an expression it yields the veto flag. order: 1

emit Name(field: value, …) fires an event: it runs every @On(Name) listener in declaration order, passing the named payload fields (any you omit take the event's declared defaults). It desugars to a direct call into the event's generated function, so firing an event is as cheap as calling a function. For a cancellable event, emit can be used as an expression that yields the cancelled flag — 0 if no listener vetoed, 1 if one did — which is the "check the decision before acting" shape: apply the effect only when the emit returns 0.

program EmitExample {
  event cancellable BeforeSpend { amount: int = 0 }

  state EmitExampleState {
    coins: int = 50
  }

  @On(BeforeSpend) handler RejectOverdraft(emit_example_st: EmitExampleState) { if amount > emit_example_st.coins { cancel } }

  handler TrySpend(emit_example_st: mut EmitExampleState) phase Update {
    if Input.key() == 'b' {
      if emit BeforeSpend(amount: 20) == 0 { emit_example_st.coins = emit_example_st.coins - 20 }
    }
  }

  handler DrawWorld(emit_example_st: EmitExampleState) phase Render {
    Screen.clear(Color.MidnightBlue)
    Screen.draw_number(x: 4, y: 4, value: emit_example_st.coins, color: Color.Gold, scale: 1)
    Screen.show()
  }
}