[Haskell-beginners] Re: dependent types

[Felipe Lessa]

On Mon, Jul 20, 2009 at 05:46:14PM -0300, Maurí­cio wrote:
> data (Eq a) => Object a = Object a

I'd rewrite this as

newtype Object a = Object a

> instance (Named a) => Eq a where
>   (==) = equals

Be careful with this instance! (specially since this is
haskell-beginners)

> instance Named (Object Integer) where
>   type NameType (Object Integer) = Integer
>   name (Object i) = i

I'd rewrite this as

instance Eq a => Named (Object a) where
  type NameType (Object a) = a
  name (Object a) = a
instance Eq a => Eq (Object a) where
  (==) = equals


However, I guess something like

data Name n a = Name n a
instance Functor (Name n) where
  fmap f (Name n a) = Name n (f a)
instance Eq n => Named (Name n a) where
  type NameType (Name n a) = n
  name (Name n _) = n
instance Copointed (Name n) where
  -- from category-extras
  extract (Name _ a) = a

would be a whole lot more useful, no?

--
Felipe.