How to add logging to a Happstack server

Disclaimer: this post describes experience of a Happstack newbie.

A very simple (but already useful!) server in Happstack may be written like this:

import Happstack.Server
import System.Environment
import Control.Monad (when)

main = do
  args <- getArgs
  when (length args < 2) $ error "Usage: ./HelloHTTP <a directory to serve>"

  simpleHTTP nullConf $ serveDirectory EnableBrowsing ["index.htm"] (head args)

This has been pretty sufficient for my simple home page for some time, but now I want logging about who is visiting the page.

Let’s do this!