Teaser
======

Let's write a hello world app.

    {-# LANGUAGE OverloadedStrings #-}

    module Hello where

    import Pipes (yield)

    hello _ = pure (("HTTP/1.1 200 OK", []), yield "hello world\n")


Note, we are not importing any interface!

If we take a closer look at the type of `hello`:

    Prelude Hello> :t hello 
    hello
      :: (Applicative f, Data.String.IsString a, Data.String.IsString t,
          Monad m) =>
        t2 -> f ((t, [t1]), Pipes.Internal.Proxy x' x () a m ())

This is a *pure* app!

Shall we run it?

    {-# LANGUAGE OverloadedStrings #-}

    module RunHello where

    import Hello (hello)
    import Network.HTTP.Pony.Serve (run)
    import Network.HTTP.Pony.Transformer.HTTP (http)
    import Pipes.Safe (runSafeT)

    main :: IO ()
    main = (runSafeT . run "localhost" "8080" . http) hello

Test it:

    # the above files are mirrored in `./test`
    runghc -isrc -itest test/RunHello.hs
   
    # open another terminal
    curl localhost:8080 -i
    
    # output:

    > HTTP/1.1 200 OK
    >
    > hello world
 
wow ~

Exercise: write a `tcp cat`