Simple colorizer/formatter (Ocaml)

colorizer.ml

type ttyfmt =
  | Plain
  | Red
  | Green
  | Warn
  | Emph

let reset_tag = "\x1b[0m"

let start_of fmt =
  match fmt with
  | Plain -> ""
  | Red -> "\x1b[31m"
  | Green -> "\x1b[32m"
  | Warn -> "\x1b[33m"
  | Emph -> "\x1b[;1m"

let end_of fmt =
  match fmt with
  | Plain -> ""
  | _ -> reset_tag

let is_tty oc =
  let fd = Unix.descr_of_out_channel oc in
  Unix.isatty fd

let log ?(fmt = Plain) oc msg =
  let do_fmt = is_tty oc in
  let start_tag =
    match do_fmt with
    | false -> ""
    | true -> start_of fmt
    in
  let end_tag =
    match do_fmt with
    | false -> ""
    | true -> end_of fmt
    in
  Printf.fprintf oc "%s%s%s\n%!" start_tag msg end_tag

let main () =
  let oc = Unix.out_channel_of_descr Unix.stdout in
  try
    log oc "Lorem ipsum";
    log ~fmt:Red oc "dolor sit amet";
    log ~fmt:Green oc "quintinquit ne tollet";
    log ~fmt:Warn oc "lipsum dixit";
    log ~fmt:Emph oc "numquam ubi sub ubi"
  with e ->
    close_out oc;
    raise e

let () = main ()