[Haskell-cafe] Are associated types synonyms like type classes?

[Stefan Holdermans]

Brian,

> I read the easy parts of the "Associated Types with Class" and  
> "Associated Type Synonyms" papers. An associated type synonym seems  
> to kind of work similarly to a restricted form of class. In what  
> way are the two following examples different?
>
>     -- define a class with a type synonym, and a set of operations
>     class A a where
>         type B b
>         foo :: a -> B b
>
>     instance A Int where
>         type B = Bool
>         foo = (==0)
>
>     -- define two classes, and an function that .
>     class A a, B b where
>         foo :: a -> b
>
>      instance A Int, B Bool where
>           foo = (==0)

It is more like -- using multi-parameter type classed with functional  
dependencies (as found, for example, in GHC):

   class A a b | a -> b where
     foo :: a -> b

   instance A Int Bool where
     foo = (== 0)

Cheers,

   Stefan