[Haskell-cafe] TH instance code.

[Andy Stewart]

Hi all,

I have below duplicate code, but i don't know how to use TH instance code.

------------------------------> duplicate code start <------------------------------
instance Variable PageType where
    toVariant = toVariant . show
    fromVariant x = fmap (\v -> read v :: PageType) $ fromVariant x

instance Variable Int where
    toVariant = toVariant . show 
    fromVariant x = fmap (\v -> read v :: Int) $ fromVariant x

instance Variable (Maybe Char) where
    toVariant = toVariant . show 
    fromVariant x = fmap (\v -> read v :: Maybe Char) $ fromVariant x

instance Variable (Maybe Int) where
    toVariant = toVariant . show 
    fromVariant x = fmap (\v -> read v :: Maybe Int) $ fromVariant x

instance Variable ProcessID where
    toVariant = toVariant . show 
    fromVariant x = fmap (\v -> read v :: ProcessID) $ fromVariant x

instance Variable GWindowId where
    toVariant = toVariant . show
    fromVariant x = fmap (\v -> read v :: GWindowId) $ fromVariant x
------------------------------> duplicate code end   <------------------------------

Any TH expert help?

Thanks,

  -- Andy