Philipp N. wrote:
i'm trying to wrap functions (a -> b -> ... -> z) of any arity to functions of type ([String] -> y), where list of strings replaces the typed arguments.
one attempt looks like this (here written with type families, you can replace it by functional dependencies or what ever):
type family Res x type instance Res x = x type instance Res (x->y) = Res y
class Nary x where nary :: x -> [String] -> Res x
instance Nary x where nary x [] = x
instance Nary (x->y) where nary f (x:xs) = nary (f $ read x) xs
i hope you can get the idea. the problem is, that you cannot distinguish type (x->y) from z, so these instances are overlapping.
Exactly. What you want to do is most likely impossible, which I think is due to polymorphism. What type should the expressions nary id nary ($) have? Nary only works when the result is a monotype, which means that you would have to add every concrete monotype as base case instance Nary Int where nary x [] = x instance Nary Char where nary x [] = x instance Nary a => Nary [a] where nary x [] = x ... etc. Regards, apfelmus