let get_suffix filename =
try
let slen = String.length filename in
let last_idx = pred slen in
let last_dot_idx = String.rindex_from filename last_idx '.' in
if last_dot_idx < last_idx then
String.sub filename (succ last_dot_idx) (slen - last_dot_idx - 1)
else ""
with
| Not_found -> raise No_suffix