haskell monadic function

monadic.hs

import Test.HUnit

import Control.Monad
import Control.Monad.Writer
import qualified Control.Monad.State as S
import StateStack
import Control.Applicative

tests = ["liftM1" ~: (liftM (*3) $ Just 8) ~?= Just 24,
         "liftM2" ~: (return 8 >>= \ x -> Just $ (*3) x) ~?= Just 24,
         "fmap" ~: (fmap (*3) $ Just 8) ~?= Just 24,
         "liftM2" ~: (runWriter $ liftM not $ writer (True, "chickpeas")) ~?= (False, "chickpeas"),
         "listM3" ~: (S.runState $ liftM (+100) pop) [1,2,3,4] ~?= (101, [2,3,4]),
         "listM4" ~: (S.runState $ fmap (+100) pop) [1,2,3,4] ~?= (101, [2,3,4]),
         "AppFun1" ~: ((+) <$> Just 3 <*> Just 5) ~?= Just 8, -- applicative functor
         "AppFun2" ~: ((+) <$> Just 3 <*> Nothing) ~?= Nothing,
         "Fun" ~: (fmap (+ 3) $ Just 5) ~?= Just 8,
         "AppFun3" ~: (Just (+3) <*> Just 4) ~?= Just 7,
         "AppFun4" ~: (Just (+3) `ap` Just 4) ~?= Just 7,
         "AppFun5" ~: [(+1), (+2), (+3)] `ap` [10, 11] ~?= [11,12,12,13,13,14],
         "join1" ~: (join $ Just (Just 9)) ~?=  Just 9,
         "join2" ~: (join $ Just (Nothing :: Maybe Int)) ~?= Nothing,
         "join3" ~: (join (Nothing :: Maybe (Maybe Int))) ~?= Nothing,
         "join4" ~: (join [[1,2,3],[4,5,6]]) ~?= [1..6],
         "join5" ~: (runWriter . join . writer $ (writer (1, "aaa"), "bbb")) ~?=
                     (1, "bbbaaa"),
         "join6" ~: ((join $ (Right (Right 9))) :: Either String Int) ~?= Right 9,
         "join7" ~: ((join $ Right (Left "error")) :: Either String Int) ~?= Left "error"
         -- "join8" ~: (S.runState . join . S.state (\ s -> (push 10, 1:2:s)) $ [0, 0, 0])
         -- ~?= ((), [10, 1, 2, 0, 0, 0])
         ]


runTests = do
  runTestTT $ TestList tests