Why base 4.4.0.0 does not use default signatures extention (new in GHC 7.2)?

[Maciej Marcin Piechotka]

Hello,

While reading the list of changes in GHC 7.2 I noticed that default
signatures extention have been added. Therefore following code compiles:

> {-# LANGUAGE NoImplicitPrelude #-}
> {-# LANGUAGE DefaultSignatures #-}
> class Functor f where
> 	fmap :: (a -> b) -> f a -> f b
> 	default fmap :: Applicative f => (a -> b) -> f a -> f b
> 	f `fmap` m = pure f <*> m
> 	(<$) :: a -> f b -> f a
> 	(<$) = fmap . const
> 
> (<$>) = fmap
> 
> class Functor f => Pointed f where
> 	point :: a -> f a
> 	default point :: Applicative f => a -> f a
> 	point = pure
>
> class Pointed f => Applicative f where
> 	pure :: a -> f a
> 	default pure :: Monad f => a -> f a
> 	pure = return
> 	(<*>) :: f (a -> b) -> f a -> f b
> 	default (<*>) :: Monad f => f (a -> b) -> f a -> f b
> 	f <*> v = liftM2 ($) f v
> 	(*>) :: f a -> f b -> f b
> 	(*>) = liftA2 (const id)
> 	(<*) :: f a -> f b -> f a
> 	(<*) = liftA2 const
> 
> class Applicative f => Monad f where
> 	return :: a -> f a
> 	(>>=) :: f a -> (a -> f b) -> f b
> 	(>>) :: f a -> f b -> f b
> 	m >> k = m >>= const k
> 
> data List a = Empty | Cons a (List a)
> 
> instance Monad List where
> 	return x = Cons x Empty
> 	Empty >>= _ = Empty
> 	Cons x xs >>= f = Cons (f x) (xs >>= f)
> 
> test = Empty <*> Empty
> 
> ($) = \f v -> f v
> liftA2 f a b = f <$> a <*> b
> liftM2 f a b = f >>= \f' -> a >>= \a' -> b >>= \b'-> return (f' a' b')
> const a _ = a
> fix f = let x = f x in x
> error _ = fix id
> id x = x
> f . g = \x -> f (g x)

While the Functor f => (Pointed f =>) Applicative f => Monad f is still
discussed the default methods would be a step towards the goal.

Regards
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 836 bytes
Desc: This is a digitally signed message part
URL: <http://www.haskell.org/pipermail/libraries/attachments/20110922/ccedd8c8/attachment.pgp>