[Haskell-cafe] Manual type-checking in graphs: Avoidable?

Kosyrev Serge _deepfire at feelingofgreen.ru
Sat Feb 20 12:18:28 UTC 2016

Jeffrey Brown <jeffbrown.the at 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

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