ludic/examples/qdecl.ludic

# ============================================================================
# qdecl.ludic — a system whose query lives in its signature.
#
#   system CleanBattle phase LateUpdate
#     query (b, p) [Battle, Pos, {Foe}] where b.hp <= 0
#   { … }
#
# is the same thing as writing `for (b, p) in query [...] where ... { … }` around
# the whole body — the loop header just moves into the declaration. The body runs
# once per matching entity, and self() is that entity.
# ============================================================================
program QueryDecl {
  property Battle { hp: int = 0, side: int = 0 }
  property Pos { x: int = 0, y: int = 0 }
  model Foe { Battle, Pos }

  handler Seed phase Start {
    spawn Foe { Battle { hp: 3, side: 1 } }
    spawn Foe { Battle { hp: 0, side: 1 } }
    spawn Foe { Battle { hp: -2, side: 0 } }
  }

  handler CleanBattle phase LateUpdate
    query (b, p) [Battle, Pos, {Foe}] where b.hp <= 0 and b.side == 1
  {
    print_int(p.x)
    despawn self()
  }

  handler Census phase Render
    query (b) [Battle]
  {
    print_int(b.hp)
  }

  handler Bye phase Render { quit() }
}