Gas prices palindromes finder ;)

gaspal.ml

let is_palindrome f =
  let s = Format.sprintf "%.2f" f in
  let pos_dot = String.index s '.' in
  String.blit s (pos_dot + 1)  s pos_dot 2;
  let s = String.sub s 0 (String.length s - 1) in
  let l, u = ref 0, ref (String.length s - 1) in
  while !l < !u && s.[!l] = s.[!u] do
    incr l; decr u;
  done;
  !l >= !u


let find_palindromes l_min l_max price =
  let l = ref l_min in
  while !l <= l_max do
    if is_palindrome !l && is_palindrome (!l *. price) then
      Format.printf "Litres : %.2f --- Prix : %.2f@." !l (!l *. price);
    l := !l +. 0.01;
  done


let () =
  try
    let l_min = float_of_string Sys.argv.(1) in
    let l_max = float_of_string Sys.argv.(2) in
    let price = float_of_string Sys.argv.(3) in
    find_palindromes l_min l_max price
  with Invalid_argument _ | Failure _ ->
    Format.eprintf "Usage: %s l_min l_max price@." Sys.argv.(0)


(*
Local Variables:
compile-command: "ocamlopt.opt -o gaspal gaspal.ml"
End:
*)

Excellent!