Merge pull request #140 from sohang3112/master

Haskell: Hello World client and server

content/docs/examples/haskell/zeromq4-haskell/hello_world_client.md

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+---
+name: hello_world_server
+language: python
+library: pyzmq
+---
+
+```haskell
+-- This lets us conviniently use efficient ByteString to send and recieve messages
+{-# LANGUAGE OverloadedStrings #-}
+
+{-
+   Hello World client in Haskell
+   Connects REQ socket to tcp://localhost:5555
+   Sends "Hello" to server, expects "World" back
+-}
+
+import System.ZMQ4.Monadic (runZMQ, socket, connect, send, receive, Socket, Req(..))
+import Control.Monad (forM_)
+import Control.Monad.IO.Class (liftIO)
+import Data.ByteString.Char8 (pack, unpack)
+
+main :: IO ()
+main = runZMQ $ do
+    --  Socket to talk to server
+    reqSocket <- socket Req
+    connect reqSocket "tcp://localhost:5555"
+
+    --  Do 10 requests, waiting each time for a response
+    forM_ [1..10] $ \i -> do
+        liftIO $ putStrLn ("Sending request " ++ show i ++ "...")
+        send reqSocket [] (pack "Hello")
+
+        --  Get the reply
+        message <- receive reqSocket
+        liftIO $ putStrLn ("Received reply " ++ show i ++ " [" ++ unpack message ++ "]")
+```

content/docs/examples/haskell/zeromq4-haskell/hello_world_server.md

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+---
+name: hello_world_server
+language: python
+library: pyzmq
+---
+
+```haskell
+-- This lets us conviniently use efficient ByteString to send and recieve messages
+{-# LANGUAGE OverloadedStrings #-}         
+
+{-
+   Hello World server in Haskell
+   Binds REP socket to tcp://*:5555
+   Expects "Hello" from client, replies with "World"
+-}
+
+import System.ZMQ4.Monadic (runZMQ, socket, bind, send, receive, Socket, Rep(..))
+import Control.Monad (forever)
+import Control.Monad.IO.Class (liftIO)
+import Control.Concurrent (threadDelay)
+import Data.ByteString.Char8 (pack, unpack)
+
+main :: IO ()
+main = runZMQ $ do
+    repSocket <- socket Rep
+    bind repSocket "tcp://*:5555"
+    forever $ do
+        --  Wait for next request from client
+        message <- receive repSocket
+        liftIO $ putStrLn ("Received request: " ++ unpack message)
+
+        --  Do some 'work' (waiting for 1 second here)
+        liftIO $ threadDelay (1 * 1000000)
+
+        --  Send reply back to client
+        send repSocket [] (pack "World")
+```

content/docs/examples/haskell/zeromq4-haskell/index.md

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+---
+headless: true
+---