applicative and choice infix operators

sequence.ml

@@ -49,8 +49,8 @@ let from_fun f =
 let empty = fun k -> ()
 
 let singleton x k = k x
-
 let return x k = k x
+let pure f k = k f
 
 (** Infinite sequence of the same element *)
 let repeat x = fun k -> while true do k x done
@@ -701,6 +701,11 @@ module Infix = struct
   let (>>=) x f = flat_map f x
 
   let (>|=) x f = map f x
+
+  let (<*>) funs args k =
+    funs (fun f -> args (fun x -> k (f x)))
+
+  let (<+>) = append
 end
 
 include Infix

sequence.mli

@@ -79,6 +79,9 @@ val singleton : 'a -> 'a t
 val return : 'a -> 'a t
   (** Synonym to {!singleton} *)
 
+val pure : 'a -> 'a t
+  (** Synonym to {!singleton} *)
+
 val repeat : 'a -> 'a t
   (** Infinite sequence of the same element. You may want to look
       at {!take} if you iterate on it. *)
@@ -442,6 +445,12 @@ module Infix : sig
 
   val (>|=) : 'a t -> ('a -> 'b) -> 'b t
     (** Infix version of {!map} *)
+
+  val (<*>) : ('a -> 'b) t -> 'a t -> 'b t
+    (** Applicative operator (product+application) *)
+
+  val (<+>) : 'a t -> 'a t -> 'a t
+    (** Concatenation of sequences *)
 end
 
 include module type of Infix