Yi Config with Hello World Ex Command

yi.hs

import Yi
import Yi.Keymap.Vim (keymapSet, mkKeymapSet, defVimConfig, vimExCommandParsers)
import qualified Yi.Mode.Haskell as Haskell
import Yi.Style
import Yi.Style.Library

-- For Ex command
import qualified Text.ParserCombinators.Parsec as P
import Yi.Keymap
import Yi.Keymap.Vim.Ex.Types
import qualified Yi.Keymap.Vim.Ex.Commands.Common as Common

defaultVimUiTheme :: Theme
defaultVimUiTheme = defaultTheme  `override` \super self -> super {
        selectedStyle = modelineFocusStyle self
 }

myConfigUI :: UIConfig
myConfigUI = (configUI defaultVimConfig)  {
        configFontSize = Just 10,
        configTheme = defaultVimUiTheme,
        configWindowFill = '~'
 }

main :: IO ()
main = yi $ defaultVimConfig {
    configUI = myConfigUI,
    defaultKm = mkKeymapSet $ defVimConfig `override` \ super self -> super
            { vimExCommandParsers = myExCmdParsers ++ vimExCommandParsers super }
 }

-- A custom macro
helloWorld :: YiM ()
helloWorld = withBuffer $ insertN "Hello, world!"

-- helloWorld Ex Command
parse :: String -> Maybe ExCommand
parse = Common.parse $ do
    P.string "helloWorld"
    return $! Common.impureExCommand {
        cmdAction = YiA $ helloWorld
      , cmdShow = "helloWorld"
      }

myExCmdParsers = [parse]