diff --git a/tools/match.ml b/tools/match.ml
new file mode 100644
index 0000000..0eaa244
--- /dev/null
+++ b/tools/match.ml
@@ -0,0 +1,108 @@
+type cls = Kw | Kl | Ks | Kd
+type op_base =
+  | Oadd
+  | Osub
+  | Omul
+type op = cls * op_base
+
+type atomic_pattern =
+  | Any
+  | Con of int64
+
+type pattern =
+  | Bnr of op * pattern * pattern
+  | Unr of op * pattern
+  | Atm of atomic_pattern
+
+let rec pattern_match p w =
+  match p with
+  | Atm (Any) -> true
+  | Atm (Con _) -> w = p
+  | Unr (o, pa) ->
+      begin match w with
+      | Unr (o', wa) ->
+          o' = o &&
+          pattern_match pa wa
+      | _ -> false
+      end
+  | Bnr (o, pl, pr) ->
+      begin match w with
+      | Bnr (o', wl, wr) ->
+          o' = o &&
+          pattern_match pl wl &&
+          pattern_match pr wr
+      | _ -> false
+      end
+
+let test_pattern_match =
+  let pm = pattern_match
+  and nm = fun x y -> not (pattern_match x y)
+  and o = (Kw, Oadd) in
+  begin
+    assert (pm (Atm Any) (Atm (Con 42L)));
+    assert (pm (Atm Any) (Unr (o, Atm Any)));
+    assert (nm (Atm (Con 42L)) (Atm Any));
+    assert (pm (Unr (o, Atm Any))
+               (Unr (o, Atm (Con 42L))));
+    assert (nm (Unr (o, Atm Any))
+               (Unr ((Kl, Oadd), Atm (Con 42L))));
+    assert (nm (Unr (o, Atm Any))
+               (Bnr (o, Atm (Con 42L), Atm Any)));
+  end
+
+type cursor = (* a position inside a pattern *)
+  | Bnrl of op * cursor * pattern
+  | Bnrr of op * pattern * cursor
+  | Unra of op * cursor
+  | Top
+
+let rec fold_cursor c p =
+  match c with
+  | Bnrl (o, c', p') -> fold_cursor c' (Bnr (o, p, p'))
+  | Bnrr (o, p', c') -> fold_cursor c' (Bnr (o, p', p))
+  | Unra (o, c') -> fold_cursor c' (Unr (o, p))
+  | Top -> p
+
+let peel p =
+  let once out (c, p) =
+    match p with
+    | Atm _ -> (c, p) :: out
+    | Unr (o, pa) ->
+        (Unra (o, c), pa) :: out
+    | Bnr (o, pl, pr) ->
+        (Bnrl (o, c, pr), pl) ::
+        (Bnrr (o, pl, c), pr) :: out
+  in
+  let rec go l =
+    let l' = List.fold_left once [] l in
+    if List.length l' = List.length l
+    then l
+    else go l'
+  in go [(Top, p)]
+
+let test_peel =
+  let o = Kw, Oadd in
+  let p = Bnr (o, Bnr (o, Atm Any, Atm Any),
+                  Atm (Con 42L)) in
+  let l = peel p in
+  let () = assert (List.length l = 3) in
+  let atomic_p (_, p) =
+    match p with Atm _ -> true | _ -> false in
+  let () = assert (List.for_all atomic_p l) in
+  let l = List.map (fun (c, p) -> fold_cursor c p) l in
+  let () = assert (List.for_all ((=) p) l) in
+  ()
+
+(* we want to compute all the configurations we could
+ * possibly be in when processing a block of instructions;
+ * to do so, we start with all the possible cursors for
+ * the list of patterns we are given, this will be our
+ * main "initial state"; each constant (used in the
+ * patterns) also generates a state of its own
+ *
+ * to create new states we can take pairs of states, and
+ * combine them with binary operations, we keep the
+ * result if it is non-trivial (non-empty) and new (we
+ * have not seen this cursor combination yet); we can
+ * also do the same with unary operations
+ * *)