diff --git a/.gitignore b/.gitignore
index 2d4daa4..267a74c 100755
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1,4 @@
 .idea*
+fenv
+*.o
+*.hi
diff --git a/12-functors-applicative-functors-and-monoids.hs b/12-functors-applicative-functors-and-monoids.hs
new file mode 100644
index 0000000..8a461b6
--- /dev/null
+++ b/12-functors-applicative-functors-and-monoids.hs
@@ -0,0 +1,18 @@
+-- Functor:
+-- :t (replicate 3)
+(replicate 3) :: a -> [a]
+
+-- :t fmap (replicate 3)
+(fmap (replicate 3)) :: f a -> f [a]
+
+-- We say that (replicate 3) has been "lifted" to f
+
+-- Also think of functors as things that output values.
+-- fmap'ing a functor is attaching a modifier to the output(s) of the functor
+-- partial applications of a function are themselves functors
+-- fmap'ing these partial applications results in composition!
+
+-- Applicative functors - Applicative class in Haskell
+class (Functor f) => Applicative f where
+  pure :: a -> f a
+  (<*>) :: f (a -> b) -> (f a -> f b)
diff --git a/fenv.hs b/fenv.hs
index 6cdef91..7c17499 100644
--- a/fenv.hs
+++ b/fenv.hs
@@ -1,6 +1,7 @@
 import System.Environment
 import System.Directory
 import System.IO
+import System.Exit (exitSuccess,exitFailure)
 import Data.List
 
 type EnvKey = String
@@ -11,23 +12,49 @@ data EnvFile =
     | Entry EnvKey EnvValue EnvFile
     deriving (Show,Eq,Read)
 
-dispatch :: [(String, [String] -> IO ())]
-dispatch = [
-        ("get", cliGet),
-        ("set", cliSet),
-        ("unset", cliUnset)
-    ]
-
 main = do
-    let f = (Entry "foo" "bar" End)
-    putStrLn (show f)
+    args <- getArgs
+    cliRun args
+
+cliRun :: [String] -> IO ()
+cliRun ("get":args) = cliGet args
+cliRun ("set":args) = cliSet args
+cliRun ("unset":args) = cliUnset args
+cliRun ("list":_) = cliList
+cliRun _ = cliFail "USAGE: fenv <get|set|unset> [...args]"
 
 cliGet :: [String] -> IO ()
 cliGet (name:_) = do
     env <- getEnvFile
     case (getEntry env name) of
         (Just value) -> putStrLn value
-        Nothing -> putStrLn "ERROR: No value defined"
+        Nothing -> cliFail "ERROR: No value defined"
+cliGet _ = cliFail "USAGE: fenv get <name>"
+
+cliUnset :: [String] -> IO ()
+cliUnset (name:_) = do
+  env <- getEnvFile
+  let env' = (removeEntry env name) in
+    replaceEnvFile env'
+cliUnset _ = cliFail "USAGE: fenv unset <name>"
+
+cliSet :: [String] -> IO ()
+cliSet (name:value:_) = do
+  env <- getEnvFile
+  let env' = (setEntry env name value) in
+    replaceEnvFile env'
+cliSet _ = cliFail "USAGE: fenv set <name> <value>"
+
+cliList :: IO ()
+cliList = do
+  env <- getEnvFile
+  printLevel env
+  where
+    printLevel (Entry key value rest) = putStrLn (key ++ ": " ++ value) >>= (printLevel rest)
+    printLevel End = return ()
+
+cliFail :: String -> IO ()
+cliFail message = putStrLn message >>= return exitFailure
 
 setEntry :: EnvFile -> EnvKey -> EnvValue -> EnvFile
 setEntry env key value = let env'=(removeEntry env key) in
@@ -58,7 +85,8 @@ getEnvFile :: IO EnvFile
 getEnvFile = do
     path <- getEnvFilePath
     contents <- readFile path
-    return $ read contents
+    if contents == "" then return End
+    else return $ read contents
 
 getEnvFilePath :: IO FilePath
 getEnvFilePath = do