1 files changed, 72 insertions, 17 deletions

diff --git a/lib/cStack.ml b/lib/cStack.ml
index 4fab9c1733..41ea5bf034 100644
--- a/lib/cStack.ml
+++ b/lib/cStack.ml
@@ -6,30 +6,85 @@
 (*         *       GNU Lesser General Public License Version 2.1        *)
 (************************************************************************)
 
-open CSig
-
 exception Empty = Stack.Empty
 
-type 'a t = 'a list ref
+type 'a t = {
+  mutable stack : 'a list;
+  mutable context : ('a list * 'a list) option
+}
+
+let create () = { stack = []; context = None }
+
+let push x s = s.stack <- x :: s.stack
+
+let pop = function
+  | { stack = [] } -> raise Stack.Empty
+  | { stack = x::xs } as s -> s.stack <- xs; x
+
+let top = function
+  | { stack = [] } -> raise Stack.Empty
+  | { stack = x::_ } -> x
 
-let create () = ref []
-let push x l = l := x :: !l
-let pop l = match !l with [] -> raise Stack.Empty | x::xs -> l := xs; x
-let top l = match !l with [] -> raise Stack.Empty | x::_ -> x
-let find f l = List.find f !l
-let find_map f l =
+let to_list = function
+  | { context = None; stack = s } -> s
+  | { context = Some (a,b); stack = s } -> a @ s @ b
+
+let to_lists = function
+  | { context = None; stack = s } -> [],s,[]
+  | { context = Some (a,b); stack = s } -> a,s,b
+
+let find f s = List.find f (to_list s)
+
+let find_map f s =
   let rec aux = function
   | [] -> raise Not_found
   | x :: xs -> match f x with None -> aux xs | Some i -> i
   in
-  aux !l
-let seek f accu l =
+  aux (to_list s)
+
+type ('b, 'c) seek = ('b, 'c) CSig.seek = Stop of 'b | Next of 'c
+
+let fold_until f accu s =
   let rec aux accu = function
     | [] -> raise Not_found
     | x :: xs -> match f accu x with Stop x -> x | Next i -> aux i xs in
-  aux accu !l
-let is_empty l = match !l with [] -> true | _ -> false
-let iter f l = List.iter f !l
-let clear l = l := []
-let length l = List.length !l
-let to_list l = !l
+  aux accu s.stack
+
+let is_empty = function
+  | { stack = []; context = None } -> true
+  | _ -> false
+
+let iter f = function
+  | { stack = s; context = None } -> List.iter f s
+  | { stack = s; context = Some(a,b) } ->
+        List.iter f a; List.iter f s; List.iter f b
+
+let clear s = s.stack <- []; s.context <- None
+
+let length = function
+  | { stack = s; context = None } -> List.length s
+  | { stack = s; context = Some(a,b) } ->
+        List.length a + List.length s + List.length b
+
+let focus s ~cond_top:c_start ~cond_bot:c_stop =
+  if s.context <> None then raise (Invalid_argument "CStack.focus");
+  let rec aux (a,s,b) grab = function
+    | [] -> raise (Invalid_argument "CStack.focus")
+    | x::xs when not grab ->
+        if c_start x then aux (a,s,b) true (x::xs)
+        else aux (x::a,s,b) grab xs
+    | x::xs ->
+        if c_stop x then a, x::s, xs
+        else aux (a,x::s,b) grab xs in
+  let a, stack, b = aux ([],[],[]) false s.stack in
+  s.stack <- List.rev stack;
+  s.context <- Some (List.rev a, b)
+
+let unfocus = function
+  | { context = None } -> raise (Invalid_argument "CStack.unfocus")
+  | { context = Some (a,b); stack } as s ->
+       s.context <- None;
+       s.stack <- a @ stack @ b
+
+let focused { context } = context <> None
+