Data commit

Task/Monads-Maybe-monad/Haskell/monads-maybe-monad-1.hs

@@ -0,0 +1,2 @@
+main = do print $ Just 3 >>= (return . (*2)) >>= (return . (+1))  -- prints "Just 7"
+          print $ Nothing >>= (return . (*2)) >>= (return . (+1)) -- prints "Nothing"

Task/Monads-Maybe-monad/Haskell/monads-maybe-monad-2.hs

@@ -0,0 +1,8 @@
+main = do print (do x <- Just 3
+                    y <- return (x*2)
+                    z <- return (y+1)
+		    return z)
+          print (do x <- Nothing
+                    y <- return (x*2)
+                    z <- return (y+1)
+                    return z)

Task/Monads-Maybe-monad/Haskell/monads-maybe-monad-3.hs

@@ -0,0 +1,8 @@
+main = do print (do x <- Just 3
+                    let y = x*2
+                    let z = y+1
+		    return z)
+          print (do x <- Nothing
+                    let y = x*2
+                    let z = y+1
+                    return z)

Task/Monads-Maybe-monad/Haskell/monads-maybe-monad-4.hs

@@ -0,0 +1,13 @@
+import Control.Monad ((>=>))
+
+safeVersion :: (a -> b) -> (a -> Bool) -> a -> Maybe b
+safeVersion f fnSafetyCheck x | fnSafetyCheck x = Just (f x)
+                              | otherwise       = Nothing
+
+safeReciprocal = safeVersion (1/) (/=0)
+safeRoot = safeVersion sqrt (>=0)
+safeLog = safeVersion log (>0)
+
+safeLogRootReciprocal = safeReciprocal >=> safeRoot >=> safeLog
+
+main = print $ map safeLogRootReciprocal [-2, -1, -0.5, 0, exp (-1), 1, 2, exp 1, 3, 4, 5]