ImpredicativeTypes is practically unsupported extension
on it's way to be removed from GHC:
https://mail.haskell.org/pipermail/ghc-devs/2016-September/012826.html
GHC-8.0.2-rc1 already fails to build xmonad-contrib as:
XMonad/Layout/Groups/Helpers.hs:181:22: error:
• Couldn't match type ‘G.WithID l0 Window
-> XMonad.Util.Stack.Zipper (G.Group l0 Window)
-> XMonad.Util.Stack.Zipper (G.Group l0 Window)’
with ‘G.ModifySpec’
Expected type: (G.WithID l0 Window
-> XMonad.Util.Stack.Zipper (G.Group l0 Window)
-> XMonad.Util.Stack.Zipper (G.Group l0 Window))
-> G.GroupsMessage
Actual type: G.ModifySpec -> G.GroupsMessage
• In the second argument of ‘(.)’, namely ‘G.Modify’
In the expression: sendMessage . G.Modify
In an equation for ‘wrap’: wrap = sendMessage . G.Modify
The workaround is simple: add explicit types to applications
or open-code direct application (this change).
Bug: https://github.com/xmonad/xmonad-contrib/issues/123
Signed-off-by: Sergei Trofimovich <siarheit@google.com>
