WxMaybe.hs

{-# LANGUAGE FlexibleContexts #-}
{-# OPTIONS -fno-warn-orphans #-}

module Graphics.UI.AF.WxForm.WxMaybe () where

import Graphics.UI.AF.WxForm.WxFormImplementation
import Maybe
import Char
import Control.Monad(liftM)
import qualified Graphics.UI.AF.WxForm.EditorComponent as EC
import qualified Graphics.UI.AF.General as AF
import Graphics.UI.AF.WxForm.GenericEC

instance (ECCreator a, Show a, AF.GInstanceCreator a) => ECCreator (Maybe a)
    where
    makeEC maybeX =
        case (maybeX, AF.createInstance) of
          (Just x, _)   -> makeMaybe x maybeX
          (_, Just x)   -> makeMaybe x maybeX
          _             -> makeGUIlessEC msg maybeX
        where
          msg = "Maybe's GUI could not be made as the subtype did not have a GUI."

makeMaybe :: (Show (Maybe a), ECCreator a) =>
             a
          -> MakeEC (Maybe a)
makeMaybe subX x = layoutAs (reverseGuis singleRow) $ AF.builderToCom $
    do val     <- AF.builderCom subX
       let lbl = case labelString (guiLabel val) of
                   ""     -> "Has ..."
                   (l:ls) -> "Has " ++ [toLower l] ++ ls
       justVal <- AF.addCom $ AF.label lbl  $ AF.mkCom (isJust x)
       AF.enabledWhen justVal (== True) val
       liftM (AF.mapValue oldToNew newToOld) $ merge (justVal, val)
    where
      oldToNew (True, y)  = Just y
      oldToNew (False, _) = Nothing
      newToOld _ (Just y)     = (True, y)
      newToOld (_, y) Nothing = (False, y)