Yes, that is my point. Existentials cannot be unwrapped.

On Sat, Feb 20, 2016 at 4:18 AM, Kosyrev Serge <_deepfire@feelingofgreen.ru> wrote:

Jeffrey Brown <jeffbrown.the@gmail.com> writes:
> After further study I believe existentials are not (at least alone)
> enough to solve the problem.
..
> getInt :: ShowBox -> Int
> getInt (SB i) = i
>
> will not compile, because it cannot infer that i is an Int:

You take a value of an existentially quantified type (which means it
can be anything at all, absent some extra context) and *proclaim* it
is an integer.

On what grounds should the compiler accept your optimistic restriction?

--
с уважениeм / respectfully,
Косырев Сергей

--

Jeffrey Benjamin Brown

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