HigherKindedPolymorphisms
It's full featured but has performance issues now.
Also, without structural function types, some advanced polymorhisms might not be that useful, unless you feel okay to annotate functions here and there.
I made this for using tagless-final style in Julia.
Usage
using HigherKindedPolymorphisms
abstract type VectSig end
@def_hkt VectSig{T} where T = Vector{T}
using CanonicalTraits
import FunctionWrappers: FunctionWrapper
Fn{A, B} = FunctionWrapper{B, Tuple{A}}
@trait Functor{F} begin
fmap :: [Fn{A, B}, App{F, A}] where {A, B} => App{F, B}
end
@implement Functor{VectSig} begin
fmap(f :: Fn{A, B}, a::App{VectSig, A}) where {A, B} =
B[f(e) for e in prj(a)] |> inj
end
f = Fn{Int, String)(string)
a = inj([1, 2, 3])
fmap(f, a) |> prj
#=> ["1", "2", "3"]