escape from existential quantification

Wang Meng
Fri, 28 Feb 2003 01:49:24 +0800 (GMT-8)

I understand that existentially bound types cannot escape.

For example, say we have
data Foo = forall a. Foo Int a

Then we cannot define a function
extract (Foo i a) = a

However,this limitation makes it extremly difficult to program with local
quantifications.Is there any way to by pass this?

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