I don't know if this is a bug or not, but the translation to type families works: class Foo a where type FooT a :: * instance Foo Int where type FooT Int = Float f :: Int -> FooT Int f = undefined g :: Int -> Float g = undefined h :: Int -> FooT Int h = g You don't even need the class contexts. Erik On Thu, Sep 13, 2012 at 11:18 AM, satvik chauhan <mystic.satvik@gmail.com> wrote:

Consider the code below :

{-# LANGUAGE MultiParamTypeClasses,FlexibleInstances,FunctionalDependencies,UndecidableInstances,FlexibleContexts #-} class Foo a c | a -> c instance Foo Int Float f :: (Foo Int a) => Int -> a f = undefined

Now when I see the inferred type of f in ghci

...

:t f

...

f :: Int -> Float

Now If I add the following code

g :: Int -> Float g = undefined

h :: (Foo Int a) => Int -> a h = g

I get the error

Could not deduce (a ~ Float)

I am not able to understand what has happened here ? The restriction "Foo Int a" should have restricted the type of h to "Int -> Float" as shown in the inferred type of f.

- Satvik

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