ludic/examples/lang/annotations.ludic

# annotations.ludic — the annotation-first style. Behaviour is expressed with
# @-decorators that desugar to plain handlers, queries and expressions, so the
# properties stay pure data and the data-oriented model is untouched.

@Handles(Move)
program RPG2D {
  property Transform { x: int = 0, y: int = 0, scale: int = 1 }
  property Velocity {
    dx: int = 0
    dy: int = 0
    @Computed speed2: int = dx * dx + dy * dy      # derived; no storage, inlined at use
  }
  model Actor { Transform, Velocity }

  # A constructor: every Actor starts visible. Runs at spawn with the model's
  # properties bound by name — no per-frame cost, no observer machinery.
  @OnSpawn(Actor)
  handler InitActor { Transform.scale = 2 }

  handler Spawn phase Start {
    spawn Actor { Transform { x: 0 }  Velocity { dx: 3, dy: 4 } }
    spawn Actor { Transform { x: 0 }  Velocity { dx: 0, dy: 0 } }
  }

  # Move every Actor whose scale is positive and that is actually moving. The
  # query is the decorator; each bound property is addressed by its own name.
  @Queries(these: [Transform{scale > 0}, Velocity{dx > 0 or dy > 0}], on: Actor)
  handler Move phase Update {
    Transform.x = Transform.x + Velocity.dx
    Transform.y = Transform.y + Velocity.dy
  }

  handler Report phase Render {
    for (t, v) in query [Transform, Velocity] { print(t.x); print(v.speed2) }
    quit()
  }
}