Re: [Haskell-beginners] Type unions

Woah, I was talking crap. Ignore my last post. On 14 December 2010 21:56, Hector Guilarte wrote:

...

data A = B Int now suppose you have a data C which has a constructor named A and a Int data C = A Int

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 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 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 _______________________________________________ Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners

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