Plan 9 from Bell Labs’s /usr/web/sources/contrib/fernan/nhc98/src/prelude/Prelude/Enum_Unit.hs
module Prelude(Enum(..)) where instance Enum () where fromEnum () = 0 toEnum n | n==0 = () toEnum n = error ("Prelude.Enum_Prelude.Unit_toEnum on " ++ show n) enumFrom n = [()] enumFromThen n n' = [()]