[Haskell-cafe] Are associated types synonyms like type classes?
bulat.ziganshin at gmail.com
Fri Sep 1 13:26:21 EDT 2006
Friday, September 1, 2006, 8:32:55 PM, you wrote:
> 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)
where you've find such unusual syntax? :) GHC/Hugs supports
multi-parameter type classes (MPTC):
class AB a b where
foo :: a -> b
instance AB Int Bool where
foo = (==0)
AT replaces MPTC with FD (functional dependency), which allows to
specify which type parameter of MPTC is detremined by another one, i.e.:
class AB a b | a->b where ....
for further details about MPTC+FD see chapter 7.1.1 in the
> Also, has anybody written a paper on the differences between
> typeclasses + associated types and ML's module system + overloading?
"ML Modules and Haskell Type Classes: A Constructive Comparison"
Bulat mailto:Bulat.Ziganshin at gmail.com
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