ludic/examples/lang/toggle.ludic

# toggle.ludic — enable/disable at the three ECS scopes, each a plain statement.
# Disabling never destroys data: a property's values persist in storage, so a
# later `enable` restores them. Queries already skip a cleared flag, so nothing
# else in the language needs to know. Running it prints: 6 0 7 1 0
#
#   disable P on e   clears one entity's has-flag   (@OnDisable / @OnEnable fire)
#   disable Model    flips the model's enabled flag (its entities drop from queries)
#   disable Handler  flips the handler's enabled flag (it stops running each phase)
program Toggles {
  property Health { hp: int = 0, max: int = 100 }
  property Shield { amount: int = 0 }
  model Player { Health, Shield }

  # hooks run at the toggle point with the property's data bound by name
  @OnDisable(Shield) handler Down { print(Shield.amount + 1) }   # 5 + 1
  @OnEnable(Shield)  handler Up   { print(Shield.amount + 2) }   # 5 + 2

  handler Seed phase Start { spawn Player { Health { max: 50 }, Shield { amount: 5 } } }

  handler Run phase Render {
    for (e) in query [Player] { disable Shield on self() }   # @OnDisable -> 6
    var n = 0
    for (s) in query [Shield] { n += 1 }
    print(n)                                             # 0 — no live Shield now

    for (e) in query [Player] { enable Shield on self() }    # @OnEnable -> 7, data intact
    n = 0
    for (s) in query [Shield] { n += 1 }
    print(n)                                             # 1 — amount is still 5

    disable Player                                           # whole model off
    n = 0
    for (p) in query [Player] { n += 1 }
    print(n)                                             # 0 — model disabled
    quit()
  }
}