diff --git a/splayMap.ml b/splayMap.ml
index d0afedbe..457baf65 100644
--- a/splayMap.ml
+++ b/splayMap.ml
@@ -29,6 +29,7 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 http://www.cs.cornell.edu/Courses/cs3110/2009fa/recitations/rec-splay.html
 *)
 
+(** {2 Polymorphic Maps} *)
 
 type ('a, 'b) t = {
   cmp : 'a -> 'a -> int;
@@ -196,3 +197,216 @@ let to_seq t =
 
 let of_seq t seq =
   Sequence.fold (fun t (k, v) -> add t k v) t seq
+
+(** {2 Functorial interface} *)
+
+module type S = sig
+  type key
+  type 'a t
+    (** Tree with keys of type [key] and values of type 'a *)
+
+  val empty : unit -> 'a t
+    (** Empty tree *)
+
+  val is_empty : _ t -> bool
+    (** Is the tree empty? *)
+
+  val find : 'a t -> key -> 'a
+    (** Find the element for this key, or raises Not_found *)
+
+  val mem : _ t -> key -> bool
+    (** Is the key member of the tree? *)
+
+  val add : 'a t -> key -> 'a -> 'a t
+    (** Add the binding to the tree *)
+
+  val singleton : key -> 'a -> 'a t
+    (** Singleton map *)
+
+  val remove : 'a t -> key -> 'a t
+    (** Remove the binding for this key *)
+
+  val iter : 'a t -> (key -> 'a -> unit) -> unit
+    (** Iterate on bindings *)
+
+  val fold : 'a t -> 'c -> ('c -> key -> 'a -> 'c) -> 'c
+    (** Fold on bindings *)
+
+  val size : _ t -> int
+    (** Number of bindings (linear) *)
+
+  val choose : 'a t -> (key * 'a)
+    (** Some binding, or raises Not_found *)
+
+  val to_seq : 'a t -> (key * 'a) Sequence.t
+
+  val of_seq : 'a t -> (key * 'a) Sequence.t -> 'a t
+end
+
+module type ORDERED = sig
+  type t
+  val compare : t -> t -> int
+end
+
+module Make(X : ORDERED) = struct
+
+  type key = X.t
+  type 'a t = {
+    mutable tree : 'a tree;  (* for lookups *)
+  } (** Tree with keys of type key, and values of type 'a *)
+  and 'a tree =
+    | Empty
+    | Node of (key * 'a * 'a tree * 'a tree)
+
+  let empty () =
+    { tree = Empty; }
+
+  let is_empty t =
+    match t.tree with
+    | Empty -> true
+    | Node _ -> false
+
+  (** Pivot the tree so that the node that has key [key], or close to [key], is
+      the root node. *)
+  let rec splay (k, v, l, r) key =
+    let c = X.compare key k in
+    if c = 0
+      then (k, v, l, r) (* found *)
+    else if c < 0
+      then match l with
+      | Empty -> (k, v, l, r)  (* not found *)
+      | Node (lk, lv, ll, lr) ->
+        let lc = X.compare key lk in
+        if lc = 0
+          then (lk, lv, ll, Node (k, v, lr, r))  (* zig *)
+        else if lc < 0
+          then match ll with
+          | Empty -> (lk, lv, Empty, Node (k, v, lr, r)) (* not found *)
+          | Node n -> (* zig zig *)
+            let (llk, llv, lll, llr) = splay n key in
+            (llk, llv, lll, Node (lk, lv, llr, Node (k, v, lr, r)))
+        else
+          match lr with
+          | Empty -> (lk, lv, ll, Node (k, v, Empty, r))
+          | Node n -> (* zig zag *)
+            let (lrk, lrv, lrl, lrr) = splay n key in
+            (lrk, lrv, Node (lk, lv, ll, lrl), Node (k, v, lrr, r))
+    else match r with
+      | Empty -> (k, v, l, r)  (* not found *)
+      | Node (rk, rv, rl, rr) ->
+        let rc = X.compare key rk in
+        if rc = 0
+          then (rk, rv, Node (k, v, l, rl), rr)  (* zag *)
+        else if rc > 0
+          then match rr with
+          | Empty -> (rk, rv, Node (k, v, l, rl), Empty)  (* not found *)
+          | Node n ->  (* zag zag *)
+            let (rrk, rrv, rrl, rrr) = splay n key in
+            (rrk, rrv, Node (rk, rv, Node (k, v, l, rl), rrl), rrr)
+        else match rl with
+          | Empty -> (rk, rv, Node (k, v, l, Empty), rr) (* zag zig *)
+          | Node n ->  (* zag zig *)
+            let (rlk, rlv, rll, rlr) = splay n key in
+            (rlk, rlv, Node (k, v, l, rll), Node (rk, rv, rlr, rr))
+
+  let find t key =
+    match t.tree with
+    | Empty -> raise Not_found
+    | Node (k, v, l, r) ->
+      let (k, v, l, r) = splay (k, v, l, r) key in
+      t.tree <- Node (k, v, l, r);   (* save balanced tree *)
+      if X.compare key k = 0
+        then v
+        else raise Not_found
+
+  let mem t key =
+    match t.tree with
+    | Empty -> false
+    | Node (k, v, l, r) ->
+      let (k, v, l, r) = splay (k, v, l, r) key in
+      t.tree <- Node (k, v, l, r);   (* save balanced tree *)
+      if X.compare key k = 0
+        then true
+        else false
+
+  (** Recursive insertion of key->value in the tree *)
+  let rec insert tree key value =
+    match tree with
+    | Empty -> Node (key, value, Empty, Empty)
+    | Node (k, v, l, r) ->
+      let c = X.compare key k in
+      if c = 0
+        then Node (key, value, l, r)  (* replace *)
+      else if c < 0
+        then Node (k, v, insert l key value, r)
+      else Node (k, v, l, insert r key value)
+
+  let add t key value =
+    let tree =
+      match t.tree with
+      | Empty -> Node (key, value, Empty, Empty)
+      | Node (k, v, l, r) ->
+        let (k, v, l, r) = splay (k, v, l, r) key in
+        let tree = Node (k, v, l, r) in
+        t.tree <- tree;  (* save balanced tree *)
+        (* insertion in this tree *)
+        insert tree key value
+    in
+    { tree; }
+
+  let singleton key value =
+    add (empty ()) key value
+
+  (** Merge of trees, where a < b *)
+  let rec left_merge a b =
+    match a, b with
+    | Empty, Empty -> Empty
+    | Node (k, v, l, r), b -> Node (k, v, l, left_merge r b)
+    | Empty, b -> b
+
+  let remove t key =
+    match t.tree with
+    | Empty -> t
+    | Node (k, v, l, r) ->
+      let (k, v, l, r) = splay (k, v, l, r) key in
+      t.tree <- Node (k, v, l, r);
+      if X.compare key k = 0
+        then (* remove the node, by merging the subnodes *)
+          let tree = left_merge l r in
+          { tree; }
+        else (* not present, same tree *)
+          t
+
+  let iter t f =
+    let rec iter t = match t with
+    | Empty -> ()
+    | Node (k, v, l, r) ->
+      iter l;
+      f k v;
+      iter r
+    in iter t.tree
+
+  let fold t acc f =
+    let rec fold acc t = match t with
+    | Empty -> acc
+    | Node (k, v, l, r) ->
+      let acc = fold acc l in
+      let acc = f acc k v in
+      fold acc r
+    in
+    fold acc t.tree
+
+  let size t = fold t 0 (fun acc _ _ -> acc+1)
+
+  let choose t =
+    match t.tree with
+    | Empty -> raise Not_found
+    | Node (k, v, _, _) -> k, v
+
+  let to_seq t =
+    Sequence.from_iter
+      (fun kont -> iter t (fun k v -> kont (k, v)))
+
+  let of_seq t seq =
+    Sequence.fold (fun t (k, v) -> add t k v) t seq
+end
diff --git a/splayMap.mli b/splayMap.mli
index f504da79..90f5d181 100644
--- a/splayMap.mli
+++ b/splayMap.mli
@@ -28,6 +28,8 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 (* TODO: map-wide operations: merge, compare, equal, for_all, exists,
         batch (sorted) add, partition, split, max_elt, min_elt, map... *)
 
+(** {2 Polymorphic Maps} *)
+
 type ('a, 'b) t
   (** Tree with keys of type 'a, and values of type 'b *)
 
@@ -70,3 +72,55 @@ val choose : ('a, 'b) t -> ('a * 'b)
 val to_seq : ('a, 'b) t -> ('a * 'b) Sequence.t
 
 val of_seq : ('a, 'b) t -> ('a * 'b) Sequence.t -> ('a, 'b) t
+
+(** {2 Functorial interface} *)
+
+module type S = sig
+  type key
+  type 'a t
+    (** Tree with keys of type [key] and values of type 'a *)
+
+  val empty : unit -> 'a t
+    (** Empty tree *)
+
+  val is_empty : _ t -> bool
+    (** Is the tree empty? *)
+
+  val find : 'a t -> key -> 'a
+    (** Find the element for this key, or raises Not_found *)
+
+  val mem : _ t -> key -> bool
+    (** Is the key member of the tree? *)
+
+  val add : 'a t -> key -> 'a -> 'a t
+    (** Add the binding to the tree *)
+
+  val singleton : key -> 'a -> 'a t
+    (** Singleton map *)
+
+  val remove : 'a t -> key -> 'a t
+    (** Remove the binding for this key *)
+
+  val iter : 'a t -> (key -> 'a -> unit) -> unit
+    (** Iterate on bindings *)
+
+  val fold : 'a t -> 'c -> ('c -> key -> 'a -> 'c) -> 'c
+    (** Fold on bindings *)
+
+  val size : _ t -> int
+    (** Number of bindings (linear) *)
+
+  val choose : 'a t -> (key * 'a)
+    (** Some binding, or raises Not_found *)
+
+  val to_seq : 'a t -> (key * 'a) Sequence.t
+
+  val of_seq : 'a t -> (key * 'a) Sequence.t -> 'a t
+end
+
+module type ORDERED = sig
+  type t
+  val compare : t -> t -> int
+end
+
+module Make(X : ORDERED) : S with type key = X.t