gistfile1.txt

data GUIEvent = KeyDownEvent { key_down__ctrl :: !Bool
                             , key_down__shift :: !Bool
                             , key_down__code :: !Int }
              | MouseEvent { mouse__x :: !Int
                           , mouse__y ::!Int }
                  deriving (Show)


instance FromJSON GUIEvent where
  parseJSON (Data.Aeson.Object v) = KeyDownEvent <$>
                                    v .: (pack "ctrlKey") <*>
                                    v .: (pack "shiftKey") <*>
                                    v .: (pack "keyCode")
  parseJSON _ = mzero


=============

function js_set_keydown_ (elem, cb) {
    // console.log(elem);
    elem.addEventListener(
        "keydown",
        function (evt) {
            cb({ "tag" : "KeyDownEvent",
                 "ctrlKey" : evt.ctrlKey,
                 "shiftKey" : evt.shiftKey,
                 "keyCode" : evt.keyCode });
        }, false);
}