Add remaining haskell book exercises

Haskell-book/26/Exercises/app/Main.hs

@@ -0,0 +1,61 @@
+{-# LANGUAGE OverloadedStrings #-}
+
+module Main where
+
+import Control.Monad.IO.Class
+import Control.Monad.Trans.Class
+import Control.Monad.Trans.Reader
+import Data.IORef
+import qualified Data.Map as M
+import Data.Maybe (fromMaybe)
+import Data.Text.Lazy (Text)
+import qualified Data.Text.Lazy as TL
+import System.Environment (getArgs)
+import Web.Scotty.Trans ( ScottyT(..)
+                        , ActionT(..)
+                        , scottyT
+                        , get
+                        , html
+                        , param )
+
+data Config =
+    Config {
+        -- that's one, one click!
+        -- two...two clicks!
+        -- Three BEAUTIFUL clicks! ah ah ahhhh
+        counts :: IORef (M.Map Text Integer)
+      , prefix :: Text
+    }
+
+type Scotty = ScottyT Text (ReaderT Config IO)
+
+bumpBoomp :: Text
+    -> M.Map Text Integer
+    -> (M.Map Text Integer, Integer)
+bumpBoomp k m =
+    let (maybeCount, newMap) = M.insertLookupWithKey (\_ _ oldCount -> oldCount + 1) k 1 m
+    in case maybeCount of
+        Nothing -> (newMap, 1)
+        Just oldCount -> (newMap, oldCount + 1)
+
+app :: Scotty ()
+app =
+    get "/:key" $ do
+        unprefixed <- param "key"
+        prefix <- lift $ asks prefix
+        let key' = mappend prefix unprefixed
+        counts <- lift $ asks counts
+        (newMap, newInteger) <- liftIO $ bumpBoomp key' <$> readIORef counts
+        liftIO $ writeIORef counts newMap
+        html $ mconcat [ "<h1>Success! Count was: "
+                       , TL.pack $ show (newInteger :: Integer)
+                       , "</h1>"
+                       ]
+
+main :: IO ()
+main = do
+    [prefixArg] <- getArgs
+    counter <- newIORef M.empty
+    let config = Config {counts = counter, prefix = TL.pack prefixArg}
+        runR = flip runReaderT config
+    scottyT 3000 runR app