Type signature of hoistCofree too restrictive

[andrewthad]

The type signature of hoistCofree is currently:

hoistCofree :: Functor f => (forall x. f x -> g x) -> Cofree f a -> Cofree g a

However, it can be generalized to:

hoistCofree :: Functor f => (f (Cofree g a) -> g (Cofree g a)) -> Cofree f a -> Cofree g a

[RyanGlScott]

See also #104 and #131 (especially #131 (comment)).

tl;dr Changing the type signature of hoistCofree is controversial and not necessarily a clear win.

[andrewthad]

Thanks. I had totally forgotten about the laws that hoistXXX functions were supposed to satisfy. I agree that it's better to universally quantify in this case to make sure that the argument is actually a natural transformation. Closing.