Re: [Haskell-beginners] Type unions

Thanks for the references. Glad to see this isn't an unreasonable wish. * -- Russ * On Tue, Dec 14, 2010 at 2:15 PM, Ozgur Akgun wrote:

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 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