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

Jeffrey Brown 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