Shuriken.defineExtension (baseNS) ->
  baseNS.defineMixin 'Callbacks', (mixin) ->

    mixin.callbacks: {}

    mixin.defineCallback: (key) ->
      @["on$key"]:     (callback) -> @hasCallback key, callback
      @["invoke$key"]: (args...)  -> @invokeCallbacks key, args...
      true

    mixin.hasCallback: (name, callback) ->
      callbacks: mixin.callbacks[name]?= []
      callbacks.push callback
      true

    mixin.callbacksFor: (name) ->
      existing: mixin.callbacks[name]
      if existing? then existing else []

    mixin.invokeCallbacks: (name, args...) ->
      for callback in mixin.callbacksFor(name)
        return false if callback(args...) is false
      true