30 Sep
2010
30 Sep
'10
1:08 a.m.
David, Ryan Ingram wrote:
Haskell doesn't have true type functions; what you are really saying is
instance Monad (\v -> Vect k (Monomial v))
Daniel Fischer wrote:
I think there was a theoretical reason why that isn't allowed (making type inference undecidable? I don't remember, I don't recall ...).
Indeed: type inference in the presence of type-level lambdas requires higher-order unification, which is undecidable [1]. Cheers, Stefan [1] Gérard P. Huet: The Undecidability of Unification in Third Order Logic Information and Control 22(3): 257-267 (1973)