Excerpts from tmp123's message of Wed Nov 07 19:25:59 +0100 2007:
> Hello,
> 
> The module "pa_log" proposed by Mr. Conway seems very near to the 
> objective of my previuos post.
> 
> The objective  now is expand a line like: DEBUG 3 "%d\n" 14
> to: if debug.val then logint 3 ( fun () -> Printf.printf "%d\" 14  ) 
> else ();
> 
> However, it is necessary to migrate the module to new camlpx .
> 
> Please, could someone give any advice about the current options: camlp4 
> or camlp5? PreCast? Functorial?

I would recommend camlp4+PreCast because it's easier.

However camlp4 already have a builtin module very similar (called Camlp4DebugParser).

Here is a brief introduction...

(*
 * No debugging code at all:
 *   $ camlp4o -parser Camlp4DebugParser debug_extension.ml
 *   true
 * Debugging code for lexing:
 *   $ STATIC_CAMLP4_DEBUG='lexing' camlp4o -parser Camlp4DebugParser debug_extension.ml
 *  let () =
 *    if Camlp4.Debug.mode "lexing"
 *    then Debug.printf "lexing" "TOKEN: Int %d" (2 * 21)
 *    else ()
 *  in true
 *
 * Debugging code for lexing and parsing:
 *   $ STATIC_CAMLP4_DEBUG='lexing:parsing' camlp4o -parser Camlp4DebugParser debug_extension.ml
 *   let () =
 *     if Camlp4.Debug.mode "lexing"
 *     then Debug.printf "lexing" "TOKEN: Int %d" (2 * 21)
 *     else () in
 *   let () =
 *     if Camlp4.Debug.mode "parsing"
 *     then Debug.printf "parsing" "RULE: ..."
 *     else ()
 *   in true
 *
 * Debugging code for any section:
 *  $ STATIC_CAMLP4_DEBUG='*' camlp4o -parser Camlp4DebugParser debug_extension.ml
 *  ... same output as above ...
 *
 * When you program is compiled you can use the CAMLP4_DEBUG variable to
 * activate some debugging sections.
 *
 * CAMLP4_DEBUG_FILE manage where messages goes (default is stderr).
 *)

camlp4_debug lexing  "TOKEN: Int %d" (2 * 21) in
camlp4_debug parsing "RULE: ..." in
true
-- 
Nicolas Pouillard aka Ertai