Add Kleisli arrows

Author: garyb

src/Control/Arrow/Kleisli.purs

@@ -0,0 +1,17 @@
+module Control.Arrow.Kleisli where
+
+import Control.Arrow
+import Data.Tuple (Tuple(..), swap)
+
+data Kleisli m a b = Kleisli (a -> m b)
+
+runKleisli :: forall m a b. Kleisli m a b -> a -> m b
+runKleisli (Kleisli f) = f
+
+instance categoryKleisli :: (Monad m) => Category (Kleisli m) where
+  id = Kleisli return
+  (<<<) (Kleisli f) (Kleisli g) = Kleisli (\b -> g b >>= f)
+
+instance arrowKleisli :: (Monad m) => Arrow (Kleisli m) where
+  arr f = Kleisli (return <<< f)
+  first (Kleisli f) = Kleisli \(Tuple b d) -> f b >>= \c -> return (Tuple c d)