Add Kleisli composition to Control.Monad

[dons]

Kleisli composition of monads is a foundational feature missing from the current Control.Monad library. A  recent discussion revealed solid support for its inclusion.

This patch adds:

    (>=>) :: (Monad m) => (a -> m b) -> (b -> m c) -> (a -> m c)
    (<=<) :: (Monad m) => (b -> m c) -> (a -> m b) -> (a -> m c)

Along with the useful control combinator:

    forever :: (Monad m) => m a -> m ()

 Traditionally, >=> has been written as @@, however to support the flipped version, new notation seems to be required. It should be notated that there is overlap with the Kleisli class in Control.Arrow (specifically >>>), however, short of a convenient unifying form for Arrow and Monad, a monad-specific >>> seems reasonable. To mirror >>> and =<<, infixr 1 was chosen.

Proposal period: 2 weeks. Deadline: 27th November.

The patch in its entirety:

New patches:

[Add Kleisli composition
Don Stewart <dons@cse.unsw.edu.au>**20061113015442] {
hunk ./Control/Monad.hs 40
+    , (>=>)         -- :: (Monad m) => (a -> m b) -> (b -> m c) -> (a -> m c)
+    , (<=<)         -- :: (Monad m) => (b -> m c) -> (a -> m b) -> (a -> m c)
+    , forever       -- :: (Monad m) => m a -> m ()
hunk ./Control/Monad.hs 179
+infixr 1 <=<, >=>
+
+-- | Left-to-right Kleisli composition of monads.
+(>=>)       :: Monad m => (a -> m b) -> (b -> m c) -> (a -> m c)
+f >=> g     = \x -> f x >>= g
+
+-- | Right-to-left Kleisli composition of monads. '(>=>)', with the arguments flipped
+(<=<)       :: Monad m => (b -> m c) -> (a -> m b) -> (a -> m c)
+(<=<)       = flip (>=>)
+
+-- | @'forever' act@ repeats the action infinitely.
+forever     :: (Monad m) => m a -> m ()
+forever a   = a >> forever a
+
hunk ./Control/Monad.hs 310
+

[dons]

Upload patch.

[igloo]

Apparently uncontroversial; patch applied.