module Main where

import Control.Monad (msum)
import Data.Char (toLower)
import Happstack.Server (FromReqURI(..), nullConf, simpleHTTP, ok, dir, path)

data Subject = World | Haskell

sayHello :: Subject -> String
sayHello World   = "Hello, World!"
sayHello Haskell = "Greetings, Haskell!"

instance FromReqURI Subject where
    fromReqURI sub =
        case map toLower sub of
          "haskell" -> Just Haskell
          "world"   -> Just World
          _         -> Nothing

main :: IO ()
main = simpleHTTP nullConf $ dir "hello" $ path $ \subject -> ok $ (sayHello subject)