[Haskell-beginners] Heterogenous list implemented with GADT

Ken Overton koverton at lab49.com
Thu Sep 30 16:13:45 EDT 2010

On Sep 30, 2010, at 4:00 PM, Daniel Fischer wrote:
> What TG2 does is wrap a list of (henceforth) unknown type (as long as the
> type has a Show instance, and that Show instance is made available by
> pattern matching).

Thanks, that sheds some light on the usefulness of GADTs in general for me.

> To achieve something like your example, you'd need
> data TG3 where
>  MkTG3 :: Show a => a -> TG3
> xs :: [TG3]
> xs = [MkTG3 5, MkTG3 'Z', MkTG3 3.14, MkTG3 False]

Much clearer, thanks a lot.


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