Index: stdlib/arg.ml
===================================================================
--- stdlib/arg.ml	(revision 13091)
+++ stdlib/arg.ml	(working copy)
@@ -101,7 +101,7 @@
 
 let current = ref 0;;
 
-let parse_argv ?(current=current) argv speclist anonfun errmsg =
+let parse_argv_dynamic ?(current=current) argv speclist anonfun errmsg =
   let l = Array.length argv in
   let b = Buffer.create 200 in
   let initpos = !current in
@@ -120,7 +120,7 @@
       | Message s ->
           bprintf b "%s: %s.\n" progname s
     end;
-    usage_b b speclist errmsg;
+    usage_b b !speclist errmsg;
     if error = Unknown "-help" || error = Unknown "--help"
     then raise (Help (Buffer.contents b))
     else raise (Bad (Buffer.contents b))
@@ -130,7 +130,7 @@
     let s = argv.(!current) in
     if String.length s >= 1 && String.get s 0 = '-' then begin
       let action =
-        try assoc3 s speclist
+        try assoc3 s !speclist
         with Not_found -> stop (Unknown s)
       in
       begin try
@@ -209,6 +209,10 @@
   done;
 ;;
 
+let parse_argv ?(current=current) argv speclist anonfun errmsg =
+  parse_argv_dynamic ~current:current argv (ref speclist) anonfun errmsg;
+;;
+
 let parse l f msg =
   try
     parse_argv Sys.argv l f msg;
@@ -217,6 +221,14 @@
   | Help msg -> printf "%s" msg; exit 0;
 ;;
 
+let parse_dynamic l f msg =
+  try
+    parse_argv_dynamic Sys.argv l f msg;
+  with
+  | Bad msg -> eprintf "%s" msg; exit 2;
+  | Help msg -> printf "%s" msg; exit 0;
+;;
+    
 let second_word s =
   let len = String.length s in
   let rec loop n =
Index: stdlib/arg.mli
===================================================================
--- stdlib/arg.mli	(revision 13091)
+++ stdlib/arg.mli	(working copy)
@@ -92,7 +92,7 @@
     options, and exit the program.  You can override this behaviour
     by specifying your own [-help] and [--help] options in [speclist].
 *)
-
+val parse_dynamic: (string * spec * string) list ref -> (string -> unit) -> string -> unit
 val parse_argv : ?current: int ref -> string array ->
   (key * spec * doc) list -> anon_fun -> usage_msg -> unit
 (** [Arg.parse_argv ~current args speclist anon_fun usage_msg] parses
@@ -106,6 +106,12 @@
   as argument.
 *)
 
+val parse_argv_dynamic: ?current:int ref ->
+  string array ->
+  (string * spec * string) list ref -> (string -> unit) -> string -> unit
+(**
+   The spec list is a reference which could be extended dynamically
+ *)      
 exception Help of string
 (** Raised by [Arg.parse_argv] when the user asks for help. *)