Re: [Caml-list] kprintf with user formatters

[henri dubois-ferriere <henridf@gmail.com>]

this sounds interesting! could you point us to any available code
showing more of this in practice?

thanks
henri

On Fri, 16 Jul 2004 09:13:20 +0200, Jean-Christophe Filliatre
<jean-christophe.filliatre@lri.fr> wrote:
> 
> Pierre Weis writes:
>  >
>  > If I understand properly:
>  >
>  > - you want to skip the runtime time penalty of formatting the
>  > arguments to string before discarding the result,
>  > - you even want not to parse the format string,
>  > - ideally you also want NOT TO EVALUATE the reminding arguments of
>  > your printf call ?
>  >
>  > Hmm, this sounds extremely lazy to me; so this suggests thunk
>  > programming; hey, we have that in the language, so let's go!
>  >
>  > let log level thunk =
>  >  if may_log level then thunk ();;
>  >
>  > ...
>  >
>  >  log 2 (fun () ->
>  >    eprintf "Argument 1 is hard to compute %d\n" (ackermann x x))
> 
> I  also  use  the same  kind  of  trick  in  practice, with  a  little
> refinement  to avoid  building the  closure. I  introduce higher-order
> functions such as
> 
>    val if_debug : ('a -> unit) -> 'a -> unit
> 
> which behaves  like application  when the debug  flag is on  (and does
> nothing otherwise). Then you can simply write
> 
>    ...
>    if_debug eprintf "this is a message";
>    ...
> 
> I even introduce variants for functions with more than one argument to
> be able to write stuff like
> 
>    ...
>    if_debug3 eprintf "syntax tree is %a@." print_tree t;
>    ...
> 
> without addition of parentheses. I still find this very convenient and
> not obtrusive as far as style is concerned.
> 
> Hope this helps,
> --
> Jean-Christophe Filliâtre (http://www.lri.fr/~filliatr)
> 
> 
> 
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