let update_loc lexbuf file line absolute chars =
let pos = lexbuf.lex_curr_p in
let new_file = match file with
| None -> pos.pos_fname
| Some s -> s
in
lexbuf.lex_curr_p <- { pos with
pos_fname = new_file;
pos_lnum = if absolute then line else pos.pos_lnum + line;
pos_bol = pos.pos_cnum - chars;
}