jeff@jeffLenovUbu:~$ ghci -XNullaryTypeClasses
GHCi, version 7.8.4: http://www.haskell.org/ghc/  :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.
Prelude> class C
Prelude> data D = DConstructor
Prelude> instance C D

<interactive>:4:10:
    ‘C’ is applied to too many type arguments
    In the instance declaration for ‘C D’
Prelude>