xmonad-contrib--0.11.2 does not compile on GHC 7.8 rc2

What steps will reproduce the problem?
1. Install GHC 7.8-rc2
2. cabal install --with-compiler=ghc-7.8.0.20140228 xmonad-contrib

What is the expected output? What do you see instead?

I expect to see a successful compile. Instead I see:

Downloading xmonad-contrib-0.11.2...
Configuring xmonad-contrib-0.11.2...
Building xmonad-contrib-0.11.2...
Preprocessing library xmonad-contrib-0.11.2...
[  1 of 226] Compiling XMonad.Util.StringProp ( XMonad/Util/StringProp.hs, 
dist/build/XMonad/Util/StringProp.o )
[  2 of 226] Compiling XMonad.Util.Replace ( XMonad/Util/Replace.hs, 
dist/build/XMonad/Util/Replace.o )
[  3 of 226] Compiling XMonad.Util.CustomKeys ( XMonad/Util/CustomKeys.hs, 
dist/build/XMonad/Util/CustomKeys.o )
[  4 of 226] Compiling XMonad.Layout.ThreeColumns ( 
XMonad/Layout/ThreeColumns.hs, dist/build/XMonad/Layout/ThreeColumns.o )
[  5 of 226] Compiling XMonad.Layout.StackTile ( XMonad/Layout/StackTile.hs, 
dist/build/XMonad/Layout/StackTile.o )
[  6 of 226] Compiling XMonad.Layout.Spiral ( XMonad/Layout/Spiral.hs, 
dist/build/XMonad/Layout/Spiral.o )
[  7 of 226] Compiling XMonad.Layout.Roledex ( XMonad/Layout/Roledex.hs, 
dist/build/XMonad/Layout/Roledex.o )
[  8 of 226] Compiling XMonad.Layout.ResizableTile ( 
XMonad/Layout/ResizableTile.hs, dist/build/XMonad/Layout/ResizableTile.o )
[  9 of 226] Compiling XMonad.Layout.OneBig ( XMonad/Layout/OneBig.hs, 
dist/build/XMonad/Layout/OneBig.o )
[ 10 of 226] Compiling XMonad.Layout.MultiToggle ( 
XMonad/Layout/MultiToggle.hs, dist/build/XMonad/Layout/MultiToggle.o )

XMonad/Layout/MultiToggle.hs:162:9:
    Could not deduce (HList b w0)
      arising from the ambiguity check for ‘??’
    from the context (HList b w)
      bound by the type signature for
                 (??) :: HList b w => a -> b -> HCons a b
      at XMonad/Layout/MultiToggle.hs:162:9-42
    The type variable ‘w0’ is ambiguous
    In the ambiguity check for:
      forall a b w. HList b w => a -> b -> HCons a b
    To defer the ambiguity check to use sites, enable AllowAmbiguousTypes
    In the type signature for ‘??’:
      (??) :: HList b w => a -> b -> HCons a b
cabal: Error: some packages failed to install:
xmonad-contrib-0.11.2 failed during the building phase. The exception was:
ExitFailure 1

What version of the product are you using? On what operating system?

xmonad-contrib-0.11.2

Please provide any additional information below.

There are two things that need to be done. Write down the incompatibility in 
the .cabal file for xmonad-contrib and fix this in a later version.
Original issue reported on code.google.com by StevensE...@gmail.com on 7 Apr 2014 at 5:38
Merged into: #563
codehenry / xmonad

xmonad-contrib--0.11.2 does not compile on GHC 7.8 rc2 #565
