> It occasionally happens that I *know* what type is (or at least ought to be) inside
> an existential type, but unfortunately GHC doesn't, and I need to get the value out.
> This can be solved using dynamic types, for example you declare the datatype as
You can also use an unsafe cast operation i
Wang Meng wrote
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
On Thu, 27 Feb 2003 18:26:31 +
Keith Wansbrough <[EMAIL PROTECTED]> wrote:
>
> The idea is to use a type more like this:
>
> data Foo = forall a. Foo Int a (a -> (Int,Bool)) (a -> Int) (a ->
> Foo)
>
> where the functions are the operations you want to use on the data
Or else one can u
> 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
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?
