For your particular constraints, it can be as easy as:
class IsA a where
toA :: a -> A
foo' :: IsA a => a -> C
foo' = foo . toA
However, you may asking the wrong question since it smells like you're
trying to embed OO into Haskell =).
Cheers,
On Wed, Jan 16, 2013 at 1:03 PM, Thiago Negri
Hello.
How do I achieve type hierarchy in Haskell?
Suppose we have the following code:
foo :: A -> C bar :: B -> C
I want something that allow me to say that B is a subtype of A, meaning: 1. I can use a value of type A where a value of type A is needed. 2. I can use a value of type B where a value of type B is needed. 3. I can use a value of type B where a value of type A is needed. 4. I can't use a value of type A where a value of type B is needed.
What are my options?
I've thought in type classes and data types with an attribute representing the extension. Any other way to do this?
Thanks, Thiago.
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-- Felipe.