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