"Cagdas Ozgenc"
class Eq a where
(==) :: a -> a -> Bool
Why do we conlude that both of the "a" refer to the same type?
Because they have the same name? I'm sorry, but I don't think I follow you.
Apparently using different types that both belonging to class Eq results in an error. For example
65 == 'a'
Yeah, that won't work. I belive the vernacular term is "apples and oranges".
It doesn't make much sense at first, however, how do you go by implementing multiple polymorphism?
There's an extension, try e.g. ghc -fglasgow-exts (IIRC). Then you can do class Foo a b where foo :: a -> b -> Bool instance Foo Char Int where foo x y = if Char.ord x == y then True else False
Secondly, why does Haskell distinguish between a Type and a Class? There seems to be no benefit of such approach.
Say what? Types are created with the 'data' keyword, and what follows is the definition of the data type. Classes describe properties types can have (or possible relationships betwen types), and instances are concrete declarations of types having those properties. Think of it as the equivalent to 'class' and 'interface' in Jave, concrete and abstract classes in C++. Or if you're familiar with generic programming, e.g. in CLOS, that's close to what you've got here.
Thirdly, is it possible to define meta-classes in Haskell?
My dictionary fails me. What did you want to do? Probably not - a class is something that exists at compile time, the Haskell type system doesn't really support run-time typing stuff. -kzm -- If I haven't seen further, it is by standing in the footprints of giants