Hi,

I would like to write a logger in OCaml. In C++ it's pretty straightforward with macro expansion that gives correct call site (file & line):

$ cat -n cpp-logger.cpp

     1 #include <iostream>

     2

     3 #define LOG_START do {\

     4    std::cerr << __FILE__ << ":" << __LINE__ << ": "

     5 #define LOG_END std::endl; } while (0)

     6

     7 int main()

     8 {

     9    LOG_START << "Got problem!" << LOG_END;

    10    return 0;

    11 }

$ ./a.out

cpp-logger.cpp:9: Got problem!

In OCaml we have __LOC__ and __LOC_OF__:

http://caml.inria.fr/pub/docs/manual-ocaml/libref/Pervasives.html

However it's not trivial to get correct call site:

$ cat -n yahoo.ml

     1  print_string "yahoo\n";;

     2

     3  Printf.printf "__LOC__ = %s\n" __LOC__;;

     4

     5  let report s =

     6      let loc, _ = __LOC_OF__ s in

     7      Printf.printf "LOC of the expression (%s): %s\n" s loc ;;

     8

     9  report "bad bug" ;;

$ ./a.outyahoo

__LOC__ = File "yahoo.ml", line 3, characters 31-38

LOC of the expression (bad bug): File "yahoo.ml", line 6, characters 28-29

I expect line 9 but I get line 6 in OCaml. I would appreciate some help to get this working. Does it involve campl4/5 / ppx?

Thanks.

--

Kind regards,

Viet