--- /Users/bobzhang/ocaml-svn/stdlib/stream.ml	2012-10-19 15:22:55.000000000 -0400
+++ src/XStream.ml	2012-12-05 18:49:26.000000000 -0500
@@ -15,7 +15,7 @@
    the empty stream. This is type safe because the empty stream is never
    patched. *)
 
-type 'a t = { count : int; data : 'a data }
+type 'a t = { count : int; data : 'a data; (* mutable *) last: 'a option }
 and 'a data =
     Sempty
   | Scons of 'a * 'a data
@@ -32,6 +32,8 @@
 
 external count : 'a t -> int = "%field0";;
 external set_count : 'a t -> int -> unit = "%setfield0";;
+let set_last (s: 'a t) (v:'a option) =
+  Obj.set_field (Obj.repr s) 2 (Obj.repr v);;
 let set_data (s : 'a t) (d : 'a data) =
   Obj.set_field (Obj.repr s) 1 (Obj.repr d)
 ;;
@@ -112,21 +114,44 @@
 
 let rec junk s =
   match s.data with
-    Scons (_, d) -> set_count s (succ s.count); set_data s d
-  | Sgen ({curr = Some _} as g) -> set_count s (succ s.count); g.curr <- None
-  | Sbuffio b -> set_count s (succ s.count); b.ind <- succ b.ind
+    Scons (a, d) -> set_count s (succ s.count); set_data s d; set_last s (Some a) ;
+  | Sgen ({curr = Some a; _ } as g) ->
+      set_count s (succ s.count); g.curr <- None; set_last s a;
+  | Sbuffio b ->
+      set_count s (succ s.count);
+      set_last s (Some (Obj.magic b.buff.[s.count - 1]));
+      b.ind <- succ b.ind;
+
   | _ ->
       match peek s with
         None -> ()
       | Some _ -> junk s
 ;;
 
+(* don't set last field *)
+let rec fake_junk s =
+  match s.data with
+    Scons (_a, d) -> set_count s (succ s.count); set_data s d; (* set_last s (Some a) ; *)
+  | Sgen ({curr = Some _a; _ } as g) ->
+      set_count s (succ s.count); g.curr <- None; (* set_last s a; *)
+  | Sbuffio b ->
+      set_count s (succ s.count);
+      (* set_last s (Some (Obj.magic b.buff.[s.count - 1])); *)
+      b.ind <- succ b.ind;
+
+  | _ ->
+      match peek s with
+        None -> ()
+      | Some _ -> fake_junk s
+;;
+
+(* Used only in npeek, and call [fake_junk] *)
 let rec nget n s =
   if n <= 0 then [], s.data, 0
   else
     match peek s with
       Some a ->
-        junk s;
+        fake_junk s;
         let (al, d, k) = nget (pred n) s in a :: al, Scons (a, d), succ k
     | None -> [], s.data, 0
 ;;
@@ -158,10 +183,10 @@
 
 (* Stream building functions *)
 
-let from f = {count = 0; data = Sgen {curr = None; func = f}};;
+let from f = {count = 0; data = Sgen {curr = None; func = f}; last = None};;
 
 let of_list l =
-  {count = 0; data = List.fold_right (fun x l -> Scons (x, l)) l Sempty}
+  {count = 0; data = List.fold_right (fun x l -> Scons (x, l)) l Sempty; last = None}
 ;;
 
 let of_string s =
@@ -170,7 +195,9 @@
 
 let of_channel ic =
   {count = 0;
-   data = Sbuffio {ic = ic; buff = String.create 4096; len = 0; ind = 0}}
+   data = Sbuffio {ic = ic; buff = String.create 4096; len = 0; ind = 0};
+   last = None
+ }
 ;;
 
 (* Stream expressions builders *)
@@ -180,16 +207,16 @@
    when the parameter stream is forced (see update code in [get_data]
    and [peek]). *)
 
-let ising i = {count = 0; data = Scons (i, Sempty)};;
-let icons i s = {count = s.count - 1; data = Scons (i, s.data)};;
-let iapp i s = {count = i.count; data = Sapp (i.data, s)};;
-
-let sempty = {count = 0; data = Sempty};;
-let slazy f = {count = 0; data = Slazy (lazy (f()))};;
-
-let lsing f = {count = 0; data = Slazy (lazy (ising (f())))};;
-let lcons f s = {count = 0; data = Slazy (lazy (icons (f()) s))};;
-let lapp f s = {count = 0; data = Slazy (lazy(iapp (f()) s))};;
+let ising i = {count = 0; data = Scons (i, Sempty); last = None};;
+let icons i s = {count = s.count - 1; data = Scons (i, s.data); last = None};;
+let iapp i s = {count = i.count; data = Sapp (i.data, s); last = None};;
+
+let sempty = {count = 0; data = Sempty; last = None};;
+let slazy f = {count = 0; data = Slazy (lazy (f())); last = None};;
+
+let lsing f = {count = 0; data = Slazy (lazy (ising (f()))); last = None};;
+let lcons f s = {count = 0; data = Slazy (lazy (icons (f()) s)); last = None};;
+let lapp f s = {count = 0; data = Slazy (lazy(iapp (f()) s)); last = None};;
 
 (* For debugging use *)
 
@@ -217,5 +244,7 @@
       print_string ")"
   | Slazy _ -> print_string "Slazy"
   | Sgen _ -> print_string "Sgen"
-  | Sbuffio b -> print_string "Sbuffio"
+  | Sbuffio _b -> print_string "Sbuffio"
 ;;
+
+let get_last v = v.last;;

--- /Users/bobzhang/ocaml-svn/stdlib/stream.mli	2012-10-19 15:22:55.000000000 -0400
+++ src/XStream.mli	2012-12-05 19:07:46.000000000 -0500
@@ -28,7 +28,7 @@
 (** {6 Stream builders} *)
 
 val from : (int -> 'a option) -> 'a t
-(** [Stream.from f] returns a stream built from the function [f].
+(** [XStream.from f] returns a stream built from the function [f].
    To create a new stream element, the function [f] is called with
    the current stream count. The user function [f] must return either
    [Some <value>] for a value or [None] to specify the end of the
@@ -48,7 +48,7 @@
 (** {6 Stream iterator} *)
 
 val iter : ('a -> unit) -> 'a t -> unit
-(** [Stream.iter f s] scans the whole stream s, applying function [f]
+(** [Stream.iter f s] scans the whole stream s, applying function [f]
    in turn to each stream element encountered. *)
 
 
@@ -56,10 +56,10 @@
 
 val next : 'a t -> 'a
 (** Return the first element of the stream and remove it from the
-   stream. Raise Stream.Failure if the stream is empty. *)
+   stream. Raise XStream.Failure if the stream is empty. *)
 
 val empty : 'a t -> unit
-(** Return [()] if the stream is empty, else raise [Stream.Failure]. *)
+(** Return [()] if the stream is empty, else raise [XStream.Failure]. *)
 
 
 (** {6 Useful functions} *)
@@ -97,3 +97,5 @@
 val slazy : (unit -> 'a t) -> 'a t
 
 val dump : ('a -> unit) -> 'a t -> unit
+val get_last: 'a t -> 'a option
+val fake_junk: 'a t -> unit