[Haskell-beginners] Question: Data Type for user selection

[Ertugrul Soeylemez]

Brent Yorgey <byorgey at seas.upenn.edu> wrote:

> > That's a bit of a contradiction, because you are using existentials
> > yourself in your GADT.
>
> No, he isn't.
>
>    data BasicSelect a where
>      SelectionNum :: Num a => a -> BasicSelect a
>      SelectionStr :: Show a => a -> BasicSelect a
>
> 'a' shows up in the result type of both constructors, so there is no
> existential quantification going on here.

Oh, right.  How would one express this as an ADT?  Seems impossible to
me.


Greets,
Ertugrul


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