class Range g => FunctorTo f g | f -> g where fmapto :: Callable c => c a b -> f a -> g b

is how you would define that class of types in Haskell. It says "If g is a range, then a pair of types f and g satisfy the FunctorTo interface[1] when knowing f determines g, and there's an implementation of fmapto with this type".

Maybe D needs typeclasses. This thread has certainly put me off of D, because being able to write down types is really quite important to me.

[1] The Haskell class keyword is defines something closer to an interface than an OO class.