[Haskell-cafe] Re: Monad instance for partially applied type constructor?

DavidA polyomino at f2s.com
Wed Sep 29 17:15:14 EDT 2010

Ryan Ingram <ryani.spam <at> gmail.com> writes:

> Haskell doesn't have true type functions; what you are really saying is
> instance Monad (\v -> Vect k (Monomial v))

Yes, that is exactly what I am trying to say. And since I'm not allowed to say
it like that, I was trying to say it using a type synonym parameterised over v
instead. It appears that GHC won't let you use partially applied type synonyms
as type constructors for instance declarations. Is this simply because the GHC
developers didn't think anyone would want to, or is there some theoretical
reason why it's hard, or a bad idea?

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