dream

This example builds on 2-middleware by showing a visitor counter. It also prints the visit count to the log. The counter itself is stored in an ordinary global ref.

let counter = ref 0

let () =
  Dream.run
  @@ Dream.logger
  @@ (fun _ ->
    counter := !counter + 1;
    Dream.log "The count is now %i" !counter;
    Dream.respond (Printf.sprintf "You are visitor number %i!" !counter))

You may see the count go up by two each time you visit http://localhost:8080. That's probably because your browser is generating requests for /favicon.ico, which we are also answering with the same handler! In 4-router, we will see how to assign different handlers to different paths, and reply to missing resources like /favicon.ico with 404 Not Found.

When you visit http://localhost:8080, you will see this handler's own Dream.log output included in the log:

$ make
[...]
08.03.21 22:33:59.869                       REQ 6 The count is now 6

Use Dream.error, Dream.warning, Dream.info, and Dream.debug to print conditionally and with different log levels.

Where to go from here?

4-router shows how to assign different handlers to different paths.