[Haskell-cafe] ANN: exists-0.1

[Gábor Lehel]

On Tue, Feb 7, 2012 at 7:23 AM, Mikhail Vorozhtsov
<mikhail.vorozhtsov at gmail.com> wrote:
> Even better, you can write
>
> type ExistentialWith c e = (Existential e, c ~ ConstraintOf e)
>
> instead of
>
> class    (Existential e, c ~ ConstraintOf e) => ExistentialWith c e
> instance (Existential e, c ~ ConstraintOf e) => ExistentialWith c e
>
> and drop UndecidableInstances.

I actually mentioned this in the preceding point of the [snip]. The
problem is that it's not even better because you can't partially apply
it.