ludic/examples/lang/reason.ludic

# reason.ludic — LC1 reason-carrying teardown. One @OnDespawn hook, but it knows
# *why* the entity is ending: `reason: r` binds an EndReason the compiler passes
# at each teardown site. An in-world `despawn` passes EndReason.Despawned; program
# shutdown passes EndReason.Quit (every still-live entity's hook fires at exit — no
# silent deaths). The body branches on the reason, exactly as Unreal's
# EndPlay(reason) / Erlang's terminate(Reason) do.
#
# Running it prints: 503 1009
#   503    Enemy A despawned in-world (Despawned): drop its loot, 3 + 500
#   1009   Enemy B outlived the run; at quit (Quit) it skips loot, 9 + 1000
#
#   bin/x game-build bin/ludicc examples/lang/reason.ludic /tmp/reason
#   /tmp/reason </dev/null
program Reasons {
  property Health { hp: int = 0 }
  property Loot   { gold: int = 0 }
  model Enemy { Health, Loot }

  @OnDespawn(Enemy, reason: r) handler Clean {
    match r {
      EndReason.Quit => { print(Health.hp + 1000) }   # app closing — don't bother dropping loot
      _              => { print(Loot.gold + 500) }     # died in-world — drop the loot
    }
  }

  handler Seed phase Start {
    spawn Enemy { Health { hp: 7 }, Loot { gold: 3 } }   # A
    spawn Enemy { Health { hp: 9 }, Loot { gold: 4 } }   # B
  }

  handler Run phase Render {
    var first = 0
    for (e) in query [Health] {
      if first == 0 { despawn self(); first = 1 }        # despawn A -> Despawned -> 3 + 500 = 503
    }
    quit()                                               # B survives -> Quit -> 9 + 1000 = 1009
  }
}