server.re

type http;
[@bs.deriving abstract]
type req = {url: string};
type res;
[@bs.send] external _end : (res, string) => unit = "end";
type handler = (req, res) => unit;
type server;
[@bs.send] external listen : (server, int) => unit = "";
[@bs.send] external createServer : (http, handler) => server = "";
[@bs.module] external http : http = "";

let server =
  http
  |. createServer((req, res) =>
       switch (req |. urlGet) {
       | "/" => res |. _end("Frontpage")
       | "/about" => res |. _end("About")
       }
     );

server |. listen(9000);