Damn it, you tricked me into writing it:

{-# LANGUAGE DeriveDataTypeable, FlexibleInstances, MultiParamTypeClasses #-}

import Control.Arrow
import XMonad
import XMonad.StackSet

data Flippy a = Flippy (Tall a) deriving (Show, Read)
data Flip = Flip deriving Typeable
instance Message Flip

instance LayoutClass Flippy a where
    runLayout (Workspace id (Flippy tall) ms) r =
      fmap (second (fmap Flippy)) $ runLayout (Workspace id tall ms) r

    handleMessage (Flippy tall) m =
      case flip of
        Just _  -> return $ doFlip (Flippy tall)
        Nothing -> fmap (fmap Flippy) $ handleMessage tall m
      where flip = fromMessage m :: Maybe Flip
            doFlip (Flippy (Tall 1 delta frac)) = Just $ Flippy $ Tall 2 delta frac
            doFlip (Flippy (Tall _ delta frac)) = Just $ Flippy $ Tall 1 delta frac

    description _ = "Flippy"

No guarantee this works, but it compiles.

On Wed, Oct 1, 2014 at 6:10 PM, Brandon Allbery <allbery.b@gmail.com> wrote:
On Wed, Oct 1, 2014 at 7:03 PM, Devin Mullins <devin.mullins@gmail.com> wrote:

I think another option is to make a new instance of LayoutClass that is just like Tall except for also supporting this message. In fact, you should be able to delegate to Tall for most definitions. Just writing off the cuff - could be wrong.


Delegating to Tall won't work; you'd have to copy the definition and modify it, like I suggested for (|||).

--
brandon s allbery kf8nh                               sine nomine associates
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