A router sends requests to different handlers, depending on their method and path. In this example, we still serve Good morning, world! at our site root, /. But, we have a different response for GET requests to /echo/*, and we respond to everything else with 404 Not Found:

let () =
  Dream.run
  @@ Dream.logger
  @@ Dream.router [

    Dream.get "/"
      (fun _ ->
        Dream.respond "Good morning, world!");

    Dream.get "/echo/:word"
      (fun request ->
        Dream.respond (Dream.param "word" request));

  ]
  @@ fun _ ->
    Dream.empty `Not_Found

This is also our first dynamic site! A request to /echo/foo gets the response foo, and a request to /echo/bar gets bar! The syntax :word in a route creates a path parameter, which can be read with Dream.param.

The whole router is a middleware, just like Dream.logger. When none of the routes match, the router passes the request to the next handler, which is right beneath it. In this example, we just respond with 404 Not Found when that happens.

Except for the status code, the 404 Not Found response is completely empty, so it might not display well in your browser. In 8-error-page, we will decorate all error responses with an error template in one central location.

The router can do more than match simple routes:

f-static forwards all requests with a certain prefix to a static file handler.
w-scope applies middlewares to groups of routes — but only when they match.
w-subsite attaches a handler as a complete, nested sub-site, which might have its own router.

Next steps:

4-counter counts requests, and exposes a special route for getting the count.
5-echo is dynamic in another way: by reading the request body.

Up to the example index