[Haskell-cafe] Lists of Existential DT

[Daniel Peebles]

You can actually write that type with impredicative polymorphism, but it
doesn't do what you seem to want: it makes a list of polymorphic values
(i.e., universally quantified ones, not existentially).

But that's going away soon, anyway...

On Sun, Feb 28, 2010 at 1:49 PM, Yves Parès <limestrael at gmail.com> wrote:

>
>
> jkff wrote:
> >
> > Or like this, with the benefit of using lists.
> > data DrawableObj a = forall a.Drawable a => DrawableObj a
> > a <,> b = DrawableObj a : b
> > drawMany (a<,>b<,>c<,>[])
> >
>
> I like this solution, but it's a pity I think that Haskell doesn't provide
> a
> way to use types like [forall a. (Drawable a) => a], which obligates you to
> declare an extra datatype...
>
> -----
> Yves Parès
>
> Live long and prosper
> --
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> http://old.nabble.com/Lists-of-Existential-DT-tp27735354p27737144.html
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>
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