log function without evaluate arguments

[tmp123 <tmp123@menta.net>]

Hello,

In order to implement a function that prints log messages only, by
example, if a boolean flag is true, and does nothing elsewhere, I've
been reading the (long) post sequence "kprintf with user formatters"
(2004 Jun 30).

In this context, "does nothing" means not convert parameters to text nor
evaluate them.

If my understanting of the reading has been correct, one of the best
options seems to be something like (in camlp4r revised syntax, I'm more
used to it):

value log_flag = ref False;

value log e =
  if log_flag.val
  then
    Lazy.force e
  else ();

and the callers must include lines like:

log (lazy (Printf.printf "%d" (sum 1 3)));

Please, is this a good way? Some sugestions to made it better in
performance or syntax?

Thanks a lot.