Merge pull request #28 from slamdata/monadcont

Add MonadCont instance

Author: jdegoes

docs/Control.Monad.Aff.md

@@ -27,6 +27,7 @@ instance plusAff :: Plus (Aff e)
 instance alternativeAff :: Alternative (Aff e)
 instance monadPlusAff :: MonadPlus (Aff e)
 instance monadRecAff :: MonadRec (Aff e)
+instance monadContAff :: MonadCont (Aff e)
 ```
 
 #### `PureAff`

src/Control/Monad/Aff.purs

@@ -23,6 +23,7 @@ module Control.Monad.Aff
 
   import Control.Alt(Alt)
   import Control.Alternative(Alternative)
+  import Control.Monad.Cont.Class(MonadCont)
   import Control.Monad.Eff(Eff())
   import Control.Monad.Eff.Class(MonadEff, liftEff)
   import Control.Monad.Eff.Exception(Error(), EXCEPTION(), catchException, error)
@@ -179,6 +180,8 @@ module Control.Monad.Aff
                   | otherwise -> later (tailRecM f a')
           Right b -> pure b
 
+  instance monadContAff :: MonadCont (Aff e) where
+    callCC f = makeAff (\eb cb -> runAff eb cb (f \a -> makeAff (\_ _ -> cb a)))
 
   instance semigroupCanceler :: Semigroup (Canceler e) where
     append (Canceler f1) (Canceler f2) = Canceler (\e -> (||) <$> f1 e <*> f2 e)

test/Test/Main.purs

@@ -2,7 +2,8 @@ module Test.Main where
 
 import Prelude
 
-import Control.Monad.Aff (Aff(), runAff)
+import Control.Monad.Aff (Aff(), runAff, later')
+import Control.Monad.Cont.Class (callCC)
 import Control.Monad.Eff (Eff())
 import Control.Monad.Eff.Class (liftEff)
 import Control.Monad.Eff.Console (CONSOLE(), log, print)
@@ -19,5 +20,13 @@ loop n = tailRecM go n
     return (Right unit)
   go n = return (Left (n - 1))
 
+delay :: forall eff. Int -> Aff eff Unit
+delay n = callCC \cont ->
+  later' n (cont unit)
+
 main :: Eff (console :: CONSOLE, err :: EXCEPTION) Unit
-main = runAff throwException (const (pure unit)) $ loop 1000000
+main = runAff throwException (const (pure unit)) $ do
+  liftEff $ log "pre-delay"
+  delay 1000
+  liftEff $ log "post-delay"
+  loop 1000000