Yi auto switch between GUI (ie, Pango) and CLI (ie, Vty)

One possible way of having a config that will start a graphical frontend if possible, and fall back on another frontend is the following:

...
import Yi.Config.Simple
import Control.Exception (catch, SomeException)
import Graphics.UI.Gtk (initGUI)

main :: IO ()
main = do
    hasGUI <- catch (initGUI >> return True) ((const $ return False)::(SomeException -> IO Bool))
    if hasGUI
    then configMain defaultEmacsConfig setupGUI
    else configMain defaultEmacsConfig setupVty

setupGUI :: ConfigM ()
setupGUI = do
  setFrontend "pango"
  setup

setupVty :: ConfigM ()
setupVty = do
  setFrontend "vty"
  setup

setup :: ConfigM ()
setup = do
  fontSize %= Just 9
  theme %= darkBlueTheme
  ...
...