A-M baby

Task/Man-or-boy-test/Haskell/man-or-boy-test.hs

@@ -0,0 +1,11 @@
+ import Control.Monad
+ import Data.IORef
+
+ a k x1 x2 x3 x4 x5 = do r <- newIORef k
+                         let b = do k <- pred !r
+                                    a k b x1 x2 x3 x4
+                         if k <= 0 then liftM2 (+) x4 x5 else b
+     where f !r = modifyIORef r f >> readIORef r
+
+ main = a 10 #1 #(-1) #(-1) #1 #0 >>= print
+     where (#) f = f . return