diff --git a/driver/compile.ml b/driver/compile.ml
index ae7b9ccbf..7c7cf40c5 100644
--- a/driver/compile.ml
+++ b/driver/compile.ml
@@ -18,10 +18,6 @@ open Config
 open Format
 open Typedtree
 
-(* Optional preprocessor *)
-
-let pproc = ref None
-
 (* Initialize the search path.
    The current directory is always searched first,
    then the directories specified with the -I option (in command-line order),
@@ -42,32 +38,31 @@ let initial_env () =
   with Not_found ->
     fatal_error "cannot open Pervasives.cmi"
 
-(* Compile a .mli file *)
+(* Optionally preprocess a source file *)
 
-let interface sourcefile =
-  init_path();
-  let prefixname = Filename.chop_extension sourcefile in
-  let modulename = capitalize(Filename.basename prefixname) in
-  let srcfile =
-    match !pproc with
-      None -> sourcefile
-    | Some pp ->
-        let tmpfile = prefixname ^ ".ppi" in
-        let comm = pp ^ " " ^ sourcefile ^ " > " ^ tmpfile in
-        if Sys.command comm <> 0 then begin
-          Printf.eprintf "Preprocessing error\n";
-          flush stderr;
-          exit 2
-        end;
-        tmpfile
-  in
-  let ic = open_in_bin srcfile in
+let pproc = ref None
+
+let preprocess sourcefile tmpfile =
+  match !pproc with
+    None -> sourcefile
+  | Some pp ->
+      let comm = pp ^ " " ^ sourcefile ^ " > " ^ tmpfile in
+      if Sys.command comm <> 0 then begin
+        Printf.eprintf "Preprocessing error\n";
+        flush stderr;
+        exit 2
+      end;
+      tmpfile
+
+(* Parse a file or get a dumped syntax tree in it *)
+
+let parse_file inputfile parse_fun ast_magic =
+  let ic = open_in_bin inputfile in
   let is_ast_file =
     try
-      let magic = Config.ast_intf_magic_number in
-      let buffer = String.create (String.length magic) in
-      really_input ic buffer 0 (String.length magic);
-      buffer = magic
+      let buffer = String.create (String.length ast_magic) in
+      really_input ic buffer 0 (String.length ast_magic);
+      buffer = ast_magic
     with _ -> false
   in
   let ast =
@@ -77,18 +72,28 @@ let interface sourcefile =
         input_value ic
       end else begin
         seek_in ic 0;
-        Location.input_name := srcfile;
-        Parse.interface (Lexing.from_channel ic)
+        Location.input_name := inputfile;
+        parse_fun (Lexing.from_channel ic)
       end
     with x -> close_in ic; raise x
   in
   close_in ic;
+  ast
+
+(* Compile a .mli file *)
+
+let interface sourcefile =
+  init_path();
+  let prefixname = Filename.chop_extension sourcefile in
+  let modulename = capitalize(Filename.basename prefixname) in
+  let inputfile = preprocess sourcefile (prefixname ^ ".ppi") in
+  let ast = parse_file inputfile Parse.interface ast_intf_magic_number in
   let sg = Typemod.transl_signature (initial_env()) ast in
   if !Clflags.print_types then (Printtyp.signature sg; print_flush());
   Env.save_signature sg modulename (prefixname ^ ".cmi");
   match !pproc with
     None -> ()
-  | Some _ -> remove_file srcfile
+  | Some _ -> remove_file inputfile
 
 (* Compile a .ml file *)
 
@@ -100,41 +105,8 @@ let implementation sourcefile =
   init_path();
   let prefixname = Filename.chop_extension sourcefile in
   let modulename = capitalize(Filename.basename prefixname) in
-  let srcfile =
-    match !pproc with
-      None -> sourcefile
-    | Some pp ->
-        let tmpfile = prefixname ^ ".ppo" in
-        let comm = pp ^ " " ^ sourcefile ^ " > " ^ tmpfile in
-        if Sys.command comm <> 0 then begin
-          Printf.eprintf "Preprocessing error\n";
-          flush stderr;
-          exit 2
-        end;
-        tmpfile
-  in
-  let ic = open_in_bin srcfile in
-  let is_ast_file =
-    try
-      let magic = Config.ast_impl_magic_number in
-      let buffer = String.create (String.length magic) in
-      really_input ic buffer 0 (String.length magic);
-      buffer = magic
-    with _ -> false
-  in
-  let ast =
-    try
-      if is_ast_file then begin
-        Location.input_name := input_value ic;
-        input_value ic
-      end else begin
-        seek_in ic 0;
-        Location.input_name := srcfile;
-        Parse.implementation (Lexing.from_channel ic)
-      end
-    with x -> close_in ic; raise x
-  in
-  close_in ic;
+  let inputfile = preprocess sourcefile (prefixname ^ ".ppo") in
+  let ast = parse_file inputfile Parse.implementation ast_impl_magic_number in
   let objfile = prefixname ^ ".cmo" in
   let oc = open_out_bin objfile in
   try
@@ -162,7 +134,7 @@ let implementation sourcefile =
                 (Translmod.transl_implementation modulename str coercion))))));
     begin match !pproc with
       None -> ()
-    | Some _ -> remove_file srcfile
+    | Some _ -> remove_file inputfile
     end;
     close_out oc
   with x ->
diff --git a/driver/optcompile.ml b/driver/optcompile.ml
index b4223e81b..57c96370d 100644
--- a/driver/optcompile.ml
+++ b/driver/optcompile.ml
@@ -18,10 +18,6 @@ open Config
 open Format
 open Typedtree
 
-(* Optional preprocessor *)
-
-let pproc = ref None
-
 (* Initialize the search path.
    The current directory is always searched first,
    then the directories specified with the -I option (in command-line order),
@@ -43,31 +39,31 @@ let initial_env () =
   with Not_found ->
     fatal_error "cannot open Pervasives.cmi"
 
-(* Compile a .mli file *)
+(* Optionally preprocess a source file *)
 
-let interface sourcefile =
-  let prefixname = Filename.chop_extension sourcefile in
-  let modulename = capitalize(Filename.basename prefixname) in
-  let srcfile =
-    match !pproc with
-      None -> sourcefile
-    | Some pp ->
-        let tmpfile = prefixname ^ ".ppi" in
-        let comm = pp ^ " " ^ sourcefile ^ " > " ^ tmpfile in
-        if Sys.command comm <> 0 then begin
-          Printf.eprintf "Preprocessing error\n";
-          flush stderr;
-          exit 2
-        end;
-        tmpfile
-  in
-  let ic = open_in_bin srcfile in
+let pproc = ref None
+
+let preprocess sourcefile tmpfile =
+  match !pproc with
+    None -> sourcefile
+  | Some pp ->
+      let comm = pp ^ " " ^ sourcefile ^ " > " ^ tmpfile in
+      if Sys.command comm <> 0 then begin
+        Printf.eprintf "Preprocessing error\n";
+        flush stderr;
+        exit 2
+      end;
+      tmpfile
+
+(* Parse a file or get a dumped syntax tree in it *)
+
+let parse_file inputfile parse_fun ast_magic =
+  let ic = open_in_bin inputfile in
   let is_ast_file =
     try
-      let magic = Config.ast_intf_magic_number in
-      let buffer = String.create (String.length magic) in
-      really_input ic buffer 0 (String.length magic);
-      buffer = magic
+      let buffer = String.create (String.length ast_magic) in
+      really_input ic buffer 0 (String.length ast_magic);
+      buffer = ast_magic
     with _ -> false
   in
   let ast =
@@ -77,18 +73,27 @@ let interface sourcefile =
         input_value ic
       end else begin
         seek_in ic 0;
-        Location.input_name := srcfile;
-        Parse.interface (Lexing.from_channel ic)
+        Location.input_name := inputfile;
+        parse_fun (Lexing.from_channel ic)
       end
     with x -> close_in ic; raise x
   in
   close_in ic;
+  ast
+
+(* Compile a .mli file *)
+
+let interface sourcefile =
+  let prefixname = Filename.chop_extension sourcefile in
+  let modulename = capitalize(Filename.basename prefixname) in
+  let inputfile = preprocess sourcefile (prefixname ^ ".ppi") in
+  let ast = parse_file inputfile Parse.interface ast_intf_magic_number in
   let sg = Typemod.transl_signature (initial_env()) ast in
   if !Clflags.print_types then (Printtyp.signature sg; print_flush());
   Env.save_signature sg modulename (prefixname ^ ".cmi");
   match !pproc with
     None -> ()
-  | Some _ -> remove_file srcfile
+  | Some _ -> remove_file inputfile
 
 (* Compile a .ml file *)
 
@@ -99,41 +104,8 @@ let print_if flag printer arg =
 let implementation sourcefile =
   let prefixname = Filename.chop_extension sourcefile in
   let modulename = capitalize(Filename.basename prefixname) in
-  let srcfile =
-    match !pproc with
-      None -> sourcefile
-    | Some pp ->
-        let tmpfile = prefixname ^ ".ppo" in
-        let comm = pp ^ " " ^ sourcefile ^ " > " ^ tmpfile in
-        if Sys.command comm <> 0 then begin
-          Printf.eprintf "Preprocessing error\n";
-          flush stderr;
-          exit 2
-        end;
-        tmpfile
-  in
-  let ic = open_in_bin srcfile in
-  let is_ast_file =
-    try
-      let magic = Config.ast_impl_magic_number in
-      let buffer = String.create (String.length magic) in
-      really_input ic buffer 0 (String.length magic);
-      buffer = magic
-    with _ -> false
-  in
-  let ast =
-    try
-      if is_ast_file then begin
-        Location.input_name := input_value ic;
-        input_value ic
-      end else begin
-        seek_in ic 0;
-        Location.input_name := srcfile;
-        Parse.implementation (Lexing.from_channel ic)
-      end
-    with x -> close_in ic; raise x
-  in
-  close_in ic;
+  let inputfile = preprocess sourcefile (prefixname ^ ".ppo") in
+  let ast = parse_file inputfile Parse.implementation ast_impl_magic_number in
   let (str, sg, finalenv) = Typemod.type_structure (initial_env()) ast in
   if !Clflags.print_types then (Printtyp.signature sg; print_flush());
   let (coercion, crc) =
@@ -158,7 +130,7 @@ let implementation sourcefile =
   Compilenv.save_unit_info (prefixname ^ ".cmx");
   begin match !pproc with
     None -> ()
-  | Some _ -> remove_file srcfile
+  | Some _ -> remove_file inputfile
   end
 
 let c_file name =