[Haskell-beginners] Type unions

[Ozgur Akgun]

This reminds me of an old thread started by, well me :)

http://www.haskell.org/pipermail/haskell-cafe/2010-March/074805.html (sorry
for the typos)

It is not an especially enlightening thread, but contains some nice
references.

HTH,

On 14 December 2010 20:09, Russ Abbott <russ.abbott at gmail.com> wrote:

> Is there a way to get this to work?
>
>  data A = Aconstructor Int
> data B = Bconstructor Int
> data AorB = A | B
>
> f :: Int -> AorB
> f x
>   | even x     = Aconstructor x
>   | otherwise = Bconstructor x
>
>  I get this diagnostic.
>
> Couldn't match expected type `AorB' against inferred type `A'
>
>
> Since AorB is A or B, why is this not permitted?
>
> If instead I write
>
> data AorB = Aconstructor Int | Bconstructor Int
>
>
> everything works out ok. But what if I want separate types for A and B?
>
> Thanks,
> *
> -- Russ *
>
>
-- 
Ozgur Akgun
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