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Date: -- (:)
From: Basile STARYNKEVITCH <basile.starynkevitch@c...>
Subject: [Caml-list] Camlp4: varargs ie a la Printf
Dear All Camlp4-ers,

I am using OCaml 3.04 (with the standard Camlp4 3.04) I do know that
the CVS Ocaml does have a Printf.kprintf function which would make my
problem easier to solve.

My problem is how to have a sort of variadic macro.



(**** file pa_trace.ml *****)

(******
    this file provide a tracing preprocessor facility; 
   at compile time, you can preprocess with the -Tfoo flag (there can be several such flags);
   in the preprocessed source, you can code 
      trace FOO "i=%d x=%g" i x end
   which is preprocessed to 
      if (Trace.Tracing.foo) then Trace.trace Trace.Level.Foo (Printf.sprintf "i=%d x=%g" i x) ;
   if preprocessed with -Tfoo or just to the unit value
      () 
   otherwise 
  ******)


module SetOfName = Set.Make(
  struct 
    type t= string;;
    let compare s1 s2 = Pervasives.compare s1 s2 
  end);;

let trset = ref SetOfName.empty;;

(* function to add tracing *)
let add_tracing trname = 
  trset := SetOfName.add trname !trset
;;

let is_traced trname =
  (SetOfName.is_empty !trset) || (SetOfName.mem trname !trset)
;;

EXTEND
  GLOBAL: Pcaml.expr ;
  Pcaml.expr: LEVEL "top" 
  [ [ "trace" ; trid = UIDENT ; fmt = STRING ; args = LIST0 Pcaml.expr ; "end" ->
    let lctrid = String.lowercase trid in 
    Printf.eprintf "trace %s does not work yet\n" lctrid;
    if is_traced lctrid then
      <:expr< 
      if Trace.Tracing.$lid:lctrid$ 
      then Trace.trace Trace.Level.$lid:lctrid$ 
	(Printf.sprintf $str:fmt$ 
	 (**** WHAT SHOULD BE ADDED HERE? *****)
	) 
      else () 
	  >>
    else 
      <:expr< () >>
    ] ]
  ;
END;


(****** end of file *****)

My problem is to produce a quotation of a list of expressions (and not
a quotation of a list expression). What should I put in place of the
comment WHAT SHOULD BE ADDED HERE?   trace FOO "i=%d x=%g" i x end

I am not sure to understand what the antiquotation  $list:l$ is for.

With the future Ocaml I would just expand
   trace FOO "i=%d x=%g" i x end
to
   if (Trace.Tracing.foo) then Printf.kprintf (Trace.ktrace Trace.Level.Foo) "i=%d x=%g" i x

which I believe should be simpler.



Perhaps the question is easy, but it is really too hot now
here..... so I am coding poorly.

If Ocaml3.05 is out soon I might use kprintf anyway....

Otherwise if some people have some tracing or logging macros (which
they accept to share into a GPL-ed code?) I would be grateful.

Thanks.
-- 

N.B. Any opinions expressed here are only mine, and not of my organization.
N.B. Les opinions exprimees ici me sont personnelles et n engagent pas le CEA.

---------------------------------------------------------------------
Basile STARYNKEVITCH   ----  Commissariat à l Energie Atomique * France
DRT/LIST/DTSI/SLA * CEA/Saclay b.528 (p111f) * 91191 GIF/YVETTE CEDEX 
phone:+33 1,6908.6055; fax: 1,6908.8395 home: 1,4665.4553; mobile: 6,8501.2359
work email: Basile point Starynkevitch at cea point fr 
home email: Basile at Starynkevitch point net

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