[Haskell-beginners] Type unions

[Tobias Brandt]

Woah, I was talking crap. Ignore my last post.

On 14 December 2010 21:56, Hector Guilarte <hectorg87 at gmail.com> wrote:
> Hello,
> Nobody has explained you why that doesn't compile...
> Here's the deal
> Suppose you have a data A which has a constructor named B and a Int
>> data A = B Int
> now suppose you have a data C which has a constructor named A and a Int
>> data C = A Int
> that compiles because the name of your data type is different from
> the constructor,
> that is, the names of the data types and the constructors they have are in
> different
> scopes, so for doing what you want, you would need to do:
>> data A = Aconstructor Int
>> data B = Bconstructor Int
>> data AorB = A A  | B B
> Where the first A is a constructor named A and the second references a data
> type A,
> idem for B
> Hope that helps you,
> Héctor Guilarte
> On Tue, Dec 14, 2010 at 3:39 PM, 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
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>
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