Does FamInstEnv.normaliseType work for you? FamInstEnv is in the types/ directory. FamInst.tcGetFamInstEnvs may also be helpful. FamInst is in the typecheck/ directory.

Richard

On May 25, 2014, at 12:42 PM, Conal Elliott <conal@conal.net> wrote:

> I'm working on a GHC plugin in which I need to programmatically construct a coercion for an associated type, given the type function name and the type argument. For instance, I have the following class:
>
> > class Encodable a where
> >   type Encode a
> >   encode :: a -> Encode a
> >   decode :: Encode a -> a
>
> along with a type instance, say `Int -> Bool`. In a GHC plugin, how can I apply a type function to an argument type to get back the resulting type and the associated coercion? (Given the latter, I think the former comes from `coercionKind`).
>
> -- Conal

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