### ppatteries.ml [ocaml]
module Sparse = struct
  exception Parse_error of string * (int * int) * (int * int)

  let () =
    Printexc.register_printer
      (function
        | Parse_error (msg, (l1, c1), (l2, c2)) ->
          Some (Printf.sprintf "%s between %d:%d and %d:%d" msg l1 c1 l2 c2)
        | _ -> None)

  (* ... *)
end
### output.txt
Fatal error: exception Ppatteries.Sparse.Parse_error("syntax error lexing", _, _)
Raised at file "parsing.ml", line 179, characters 14-17
Called from file "str.ml", line 0, characters 0-0
Called from file "src/batList.ml", line 103, characters 17-20
Called from file "src/batStd.ml", line 226, characters 17-20