Added CFut.  Just ran into this GHC error:

[8 of 8] Compiling Control.LVish.CancelT ( Control/LVish/CancelT.hs, dist/build/Control/LVish/CancelT.o )
ghc: panic! (the 'impossible' happened)
  (GHC version 7.6.3 for x86_64-apple-darwin):
	cgLookupPanic (probably invalid Core; try -dcore-lint)
    cobox{v a2jT} [lid]
    static binds for:
    local binds for:
    par-transformers-1.1:Control.LVish.CancelT.$WCPair{v r1uO} [gid[DataConWrapper]]

Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug