Index: driver/pparse.ml
===================================================================
--- driver/pparse.ml	(revision 12564)
+++ driver/pparse.ml	(working copy)
@@ -47,6 +47,48 @@
 
 exception Outdated_version
 
+let write_ast magic ast =
+  let fn = Filename.temp_file "camlppx" "" in
+  let oc = open_out_bin fn in
+  output_string oc magic;
+  output_value oc !Location.input_name;
+  output_value oc ast;
+  close_out oc;
+  fn
+
+let apply_rewriter fn_in ppx =
+  let fn_out = Filename.temp_file "camlppx" "" in
+  let comm = Printf.sprintf "%s %s %s" ppx (Filename.quote fn_in) (Filename.quote fn_out) in
+  let ok = Ccomp.command comm = 0 in
+  Misc.remove_file fn_in;
+  if not ok then begin
+    Misc.remove_file fn_out;
+    raise Error;
+  end;
+  if not (Sys.file_exists fn_out) then raise Error;
+  fn_out
+
+let read_ast magic fn =
+  let ic = open_in_bin fn in
+  try
+    let buffer = Misc.input_bytes ic (String.length magic) in
+    if buffer <> magic then
+      Misc.fatal_error "OCaml and preprocessor have incompatible versions";
+    Location.input_name := input_value ic;
+    let ast = input_value ic in
+    close_in ic;
+    Misc.remove_file fn;
+    ast
+  with exn ->
+    close_in ic;
+    Misc.remove_file fn;
+    raise exn
+
+let apply_rewriters magic ast ppxs =
+  if ppxs = [] then ast
+  else let fn = List.fold_left apply_rewriter (write_ast magic ast) ppxs in
+  read_ast magic fn
+
 let file ppf inputfile parse_fun ast_magic =
   let ic = open_in_bin inputfile in
   let is_ast_file =
@@ -79,4 +121,4 @@
     with x -> close_in ic; raise x
   in
   close_in ic;
-  ast
+  apply_rewriters ast_magic ast !Clflags.ppx
Index: driver/main_args.mli
===================================================================
--- driver/main_args.mli	(revision 12564)
+++ driver/main_args.mli	(working copy)
@@ -44,6 +44,7 @@
     val _output_obj : unit -> unit
     val _pack : unit -> unit
     val _pp : string -> unit
+    val _ppx : string -> unit
     val _principal : unit -> unit
     val _rectypes : unit -> unit
     val _runtime_variant : string -> unit
@@ -134,6 +135,7 @@
   val _p : unit -> unit
   val _pack : unit -> unit
   val _pp : string -> unit
+  val _ppx : string -> unit
   val _principal : unit -> unit
   val _rectypes : unit -> unit
   val _runtime_variant : string -> unit
Index: driver/main.ml
===================================================================
--- driver/main.ml	(revision 12564)
+++ driver/main.ml	(working copy)
@@ -121,6 +121,7 @@
   let _output_obj () = output_c_object := true; custom_runtime := true
   let _pack = set make_package
   let _pp s = preprocessor := Some s
+  let _ppx s = ppx := s :: !ppx
   let _principal = set principal
   let _rectypes = set recursive_types
   let _runtime_variant s = runtime_variant := s
Index: driver/main_args.ml
===================================================================
--- driver/main_args.ml	(revision 12564)
+++ driver/main_args.ml	(working copy)
@@ -209,6 +209,10 @@
   "-pp", Arg.String f, "<command>  Pipe sources through preprocessor <command>"
 ;;
 
+let mk_ppx f =
+  "-ppx", Arg.String f, "<command>  Pipe abstract syntax trees through preprocessor <command>"
+;;
+
 let mk_principal f =
   "-principal", Arg.Unit f, " Check principality of type inference"
 ;;
@@ -428,6 +432,7 @@
   val _output_obj : unit -> unit
   val _pack : unit -> unit
   val _pp : string -> unit
+  val _ppx : string -> unit
   val _principal : unit -> unit
   val _rectypes : unit -> unit
   val _runtime_variant : string -> unit
@@ -517,6 +522,7 @@
   val _p : unit -> unit
   val _pack : unit -> unit
   val _pp : string -> unit
+  val _ppx : string -> unit
   val _principal : unit -> unit
   val _rectypes : unit -> unit
   val _runtime_variant : string -> unit
@@ -644,6 +650,7 @@
     mk_output_obj F._output_obj;
     mk_pack_byt F._pack;
     mk_pp F._pp;
+    mk_ppx F._ppx;
     mk_principal F._principal;
     mk_rectypes F._rectypes;
     mk_runtime_variant F._runtime_variant;
@@ -741,6 +748,7 @@
     mk_p F._p;
     mk_pack_opt F._pack;
     mk_pp F._pp;
+    mk_ppx F._ppx;
     mk_principal F._principal;
     mk_rectypes F._rectypes;
     mk_runtime_variant F._runtime_variant;
Index: driver/optmain.ml
===================================================================
--- driver/optmain.ml	(revision 12564)
+++ driver/optmain.ml	(working copy)
@@ -132,6 +132,7 @@
   let _p = set gprofile
   let _pack = set make_package
   let _pp s = preprocessor := Some s
+  let _ppx s = ppx := s :: !ppx
   let _principal = set principal
   let _rectypes = set recursive_types
   let _runtime_variant s = runtime_variant := s
Index: tools/ocamlcp.ml
===================================================================
--- tools/ocamlcp.ml	(revision 12564)
+++ tools/ocamlcp.ml	(working copy)
@@ -73,6 +73,7 @@
   let _output_obj = option "-output-obj"
   let _pack = option "-pack"
   let _pp s = incompatible "-pp"
+  let _ppx s = incompatible "-ppx"
   let _principal = option "-principal"
   let _rectypes = option "-rectypes"
   let _runtime_variant s = option_with_arg "-runtime-variant" s
Index: utils/clflags.ml
===================================================================
--- utils/clflags.ml	(revision 12564)
+++ utils/clflags.ml	(working copy)
@@ -33,6 +33,7 @@
 and classic = ref false                 (* -nolabels *)
 and nopervasives = ref false            (* -nopervasives *)
 and preprocessor = ref(None : string option) (* -pp *)
+and ppx = ref ([] : string list)        (* -ppx *)
 let annotations = ref false             (* -annot *)
 let binary_annotations = ref false      (* -annot *)
 and use_threads = ref false             (* -thread *)
Index: utils/clflags.mli
===================================================================
--- utils/clflags.mli	(revision 12564)
+++ utils/clflags.mli	(working copy)
@@ -30,6 +30,7 @@
 val classic : bool ref
 val nopervasives : bool ref
 val preprocessor : string option ref
+val ppx : string list ref
 val annotations : bool ref
 val binary_annotations : bool ref
 val use_threads : bool ref