faking universal quantification in constraints

[Edward Kmett]

On Mon, Apr 16, 2012 at 6:57 PM, Nicolas Frisby <nicolas.frisby at gmail.com>wrote:

> I'm simulating skolem variables in order to fake universal
> quantification in constraints via unsafeCoerce.
>
>  http://hpaste.org/67121
>
> I'm not familiar with various categories of types from the run-time's
> perspective, but I'd be surprised if there were NOT a way to use this
> code to create run-time errors.
>
> Is there a way to make it safer? Perhaps by making Skolem act more
> like GHC's Any type? Or perhaps like the -> type? I'd like to learn
> about the varieties of types from the run-time's perspective.
>

FWIW- I have a version of this concept packaged up in the constraints
package.

I had a small example that abused flexible instances and MPTCs to cause the
single Skolem version of my code to fail.

However, when I refined it to use two Skolem variables I wasn't able to
derive sufficient Oleggery to break it. That said, an absence of a
counter-example isn't a proof that it can't exist.

http://hackage.haskell.org/packages/archive/constraints/0.3/doc/html/src/Data-Constraint-Forall.html
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