Francesco Mazzoli <f <at> mazzo.li> writes:
>
> I have stumbled upon a strange annoyance:
>
> {-# LANGUAGE GADTs #-}
Hi Francesco, I think you'll find that the 'annoyance' is nothing to do
with GADTs. I suggest you take the type signature off of foo1, and see
what type ghc infers for it. It isn't :: a -> Foo a -> Int.
> data Foo v where
> Foo :: Foo (Maybe v)
>
> -- This doesn't work
> -- **** foo1 :: a -> Foo a -> Int
> foo1 Nothing Foo = undefined
> foo1 (Just x) Foo = undefined
...
> The first definition fails with the error
>
> Couldn't match expected type `a' with actual type `Maybe t0'
...
> In the pattern: Nothing
Yep, that message explains what's going on well enough for me.
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