CGI look-up environment variable's value in OCaml

(*
   CGI look-up environment variable's value
   http://www.cs.uvm.edu/~dvanhorn/ocaml/getenv.html
   Cf.
http://www.ccs.neu.edu/home/dorai/t-y-scheme/t-y-scheme-Z-H-19.html#node_sec_17.2
*)

let getenv env_var =
  try Sys.getenv env_var
  with Not_found -> "";;

let split c s =
  let rec loop s =
    if s = "" then []
    else try
      let i = String.index s c in
      (String.sub s 0 i)::loop (String.sub s (i+1) ((String.length s)-(i+1)))
    with Not_found ->
      s::[]
  in
  loop s;;

let args =
  List.map
    (function par_arg -> split '=' par_arg)
    (split '&' (getenv "QUERY_STRING"));;

let print_vars () =
  List.iter
    (function "envvar"::x::[] ->
      print_string x;
      print_string " = ";
      print_string (getenv x);
      print_newline())
    args;;

let main () =
  print_string "content-type: text/plain";
  print_newline();
  print_newline();
  print_newline();
  print_vars();
  exit 0;;

main();;