Working with ocaml Lwt sockets -

i have been on learning ocaml week, things got clear, others rather not. i'm trying compose simple tic-tac-toe server accepting connections via telnet. word. have use lwt , rigth seems me darken place because had faced of language pecularities. begining of code:

let sock = lwt_unix.socket unix.pf_inet unix.sock_stream 0  let setting_up_server_socket =       let sockaddr = (unix.addr_inet(unix.inet_addr_of_string "127.0.0.1", 23233)) in     lwt_unix.set_close_on_exec sock;     lwt_unix.setsockopt sock unix.so_reuseaddr true;     lwt_unix.bind sock sockaddr;     lwt_unix.listen sock 20 

ok, that's clear. server socket set listen clients connections. let's try first guest:

let handle_income =      lwt_unix.accept sock;; 

seems clear, but:

val handle_income : (lwt_unix.file_descr * lwt_unix.sockaddr) lwt.t = <abstr> 

here i'm stacked. don't know how send message client socket. unlike general unix.accept returns ('a * 'b) lwt.t. questions:

1. how can pure client "lwt_unix.file_descr" that?
2. ('a * 'b) lwt.t. tuple belonging lwt.t object, isn't it? or field? confused @ all.

p.s. sorry if english not acceptable. learning long time ago. question asked please give piece of advise, can best information ocaml. best mean short/clearness. due reading o'reilly instantly forget reading 5 min ago because it's never clear or author talking used for. ocaml quite different java , js had started with.

a value of type 'a lwt.t represents thread evaluate value of type 'a once ready (or error went wrong). way 'a 'a lwt.t bind function, called soon, 'a lwt.t thread finished , data ready. can bind lwt.bind function, available in infix notation >>=.

for example:

let process_client fd =    lwt_unix.accept fd >>= fun (cli,sock) ->   let chan = lwt_io.(of_fd ~mode:output cli) in   lwt_io.fprintf chan "hi there, , bye!" >>= fun () ->   lwt_io.close chan 

this uses infix notation, can rewrite more verbose:

let reply chan =    lwt_io.fprintf chan "hi there, , bye!"  let finish chan = lwt_io.close chan  let create_chan = lwt_io.(of_fd ~mode:output cli)  let process_client fd =    let accept_t = lwt_unix.accept fd in   let chan_t = lwt.map accept_t create_chan in   let reply_t = lwt.bind accept_t reply in    lwt.bind reply_t finish 

where _t designates thread. i.e., accept_t thread return pair of file descriptor , socket address. chan_t thread return channel (for doing buffered io).

lwt comes support special syntax. support 2 syntaxes, old camlp4 , newer 1 ppx. in old syntax, 1 can write process_client function follows:

let process_client fd =    lwt (cli,sock) = lwt_unix.accept fd in   let chan = lwt_io.(of_fd ~mode:output cli) in   lwt () = lwt_io.fprintf chan "hi there, , bye!" in   lwt_io.close chan 

there lwt special form of let not binds names values, waits them evaluate.

i hope answered questions. may find library interesting.

p.s. didn't test code, if have issues, don't hesitate ask.

p.p.s. left proper shutdown procedure, keep code simple.