## GHC Panic: No Skolem Info

GHC 7.8.3 and from git both panic with

```
Couldn't match kind ‘o1’ with ‘(,) o o’
‘o1’ is untouchable
inside the constraints (Object (c :><: c) a)
bound by a type expected by the context:
Object (c :><: c) a =>
Tagged a (c (FMap (ProductF c) a) (FMap (Proj2 c c) a))
at Product.hs:35:9-15ghc: panic! (the 'impossible' happened)
(GHC version 7.9.20140908 for x86_64-unknown-linux):
No skolem info: o1_a6XS
```

I have not yet attempted to reduce the problem at all. The offending code is the use of fmap here:

```
proj2 :: forall (c :: o -> o -> *). ProductCategory c => NatTr (c :><: c) c (ProductF c) (Proj2 c c)
proj2 = NatTr t where
NatTr t = fmap (CompF Proj2 IdentityF) e
e :: NatTr (c :><: c) (c :><: c) (Comp ('KProxy :: KProxy o) (Diag c) (ProductF c)) (IdentityF (c :><: c))
e = counit
```

fmap is defined as

```
fmap :: forall f (a :: o1) (b :: o1). Functor f ('KProxy :: KProxy (o1 -> o2)) => f -> Domain f a b -> Codomain f (FMap f a :: o2) (FMap f b :: o2)
fmap _ = proxy morphMap (Proxy :: Proxy f)
```

while CompF is defined by

```
data CompF f g (k :: KProxy (o3 -> o4, o1 -> o2)) where
CompF :: (Functor f ('KProxy :: KProxy (o3 -> o4)), Functor g ('KProxy :: KProxy (o1 -> o2))) =>
f -> g -> CompF f g ('KProxy :: KProxy (o3 -> o4, o1 -> o2))
```

This makes some sense because there is a functional dependency between the functor and the kind proxy.