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
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 -- View this message in context: http://old.nabble.com/Lists-of-Existential-DT-tp27735354p27737144.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.
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