On 01/05/07, Brandon S. Allbery KF8NH <[EMAIL PROTECTED]> wrote:
I think all this does is save you from having to write a bunch of wrappers that unwrap the contained value, do something to it, and rewrap the result.
Exactly. Basically what newtype deriving does is if you have a declaration like the following: newtype T = TConstructor M And M instantiates some class (like Monad, Functor etc), you can derive that class for T. For example, here's how the Functor instance would look for the following newtype: newtype MyMaybe a = MM (Maybe a) deriving (Functor) -- The instance looks like this: instance Functor MyMaybe where fmap f (MM a) = MM (fmap f a) The instance just unwraps and rewraps the newtype constructor. -- -David House, [EMAIL PROTECTED] _______________________________________________ Haskell-Cafe mailing list [email protected] http://www.haskell.org/mailman/listinfo/haskell-cafe
