added some typeclasses in a submodule

sequence.ml

@@ -471,6 +471,53 @@ let random_array a =
 
 let random_list l = random_array (Array.of_list l)
 
+(** {2 Type-classes} *)
+
+module TypeClass = struct
+  (** {3 Classes} *)
+  type ('a,'b) sequenceable = {
+    to_seq : 'b -> 'a t;
+    of_seq : 'a t -> 'b;
+  }
+
+  type ('a,'b) addable = {
+    empty : 'b;
+    add : 'b -> 'a -> 'b;
+  }
+
+  type 'a monoid = ('a,'a) addable
+
+  type ('a,'b) iterable = {
+    iter : ('a -> unit) -> 'b -> unit;
+  }
+
+  (** {3 Instances} *)
+
+  let (sequenceable : ('a,'a t) sequenceable) = {
+    to_seq = (fun seq -> seq);
+    of_seq = (fun seq -> seq);
+  }
+
+  let (iterable : ('a, 'a t) iterable) = {
+    iter = (fun f seq -> iter f seq);
+  }
+
+  let (monoid : 'a t monoid) = {
+    empty = empty;
+    add = (fun s1 s2 -> append s1 s2);
+  }
+
+  (** {3 Conversions} *)
+
+  let of_iterable iterable x =
+    from_iter (fun k -> iterable.iter k x)
+
+
+  let to_addable addable seq =
+    fold addable.add addable.empty seq
+end
+
+
 (** {2 Pretty printing of sequences} *)
 
 (** Pretty print a sequence of ['a], using the given pretty printer

sequence.mli

@@ -254,6 +254,38 @@ val random_array : 'a array -> 'a t
 
 val random_list : 'a list -> 'a t
 
+(** {2 Type-classes} *)
+
+module TypeClass : sig
+  (** {3 Classes} *)
+  type ('a,'b) sequenceable = {
+    to_seq : 'b -> 'a t;
+    of_seq : 'a t -> 'b;
+  }
+
+  type ('a,'b) addable = {
+    empty : 'b;
+    add : 'b -> 'a -> 'b;
+  }
+
+  type 'a monoid = ('a,'a) addable
+
+  type ('a,'b) iterable = {
+    iter : ('a -> unit) -> 'b -> unit;
+  }
+
+  (** {3 Instances} *)
+
+  val sequenceable : ('a,'a t) sequenceable
+  val iterable : ('a,'a t) iterable
+  val monoid : 'a t monoid
+
+  (** {3 Conversions} *)
+
+  val of_iterable : ('a,'b) iterable -> 'b -> 'a t
+  val to_addable : ('a,'b) addable -> 'a t -> 'b
+end
+
 (** {2 Pretty printing of sequences} *)
 
 val pp_seq : ?sep:string -> (Format.formatter -> 'a -> unit) ->