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
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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