[Haskell-beginners] Type unions

[Hector Guilarte]

Hahaha don't worry man,

Hope it helps for you too

On Tue, Dec 14, 2010 at 4:32 PM, Tobias Brandt <tob.brandt at googlemail.com>wrote:

> 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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