monad instance for CCFun

core/CCFun.ml

@@ -58,3 +58,10 @@ let finally ~h ~f =
   with e ->
     h ();
     raise e
+
+module Monad(X : sig type t end) = struct
+  type 'a t = X.t -> 'a
+  let return x _ = x
+  let (>|=) f g x = g (f x)
+  let (>>=) f g x = g (f x) x
+end

core/CCFun.mli

@@ -67,3 +67,14 @@ val finally : h:(unit -> unit) -> f:(unit -> 'a) -> 'a
   (** [finally h f] calls [f ()] and returns its result. If it raises, the
       same exception is raised; in {b any} case, [h ()] is called after
       [f ()] terminates. *)
+
+(** {2 Monad}
+
+functions with a fixed domain are monads in their codomain *)
+
+module Monad(X : sig type t end) : sig
+  type 'a t = X.t -> 'a
+  val return : 'a -> 'a t
+  val (>|=) : 'a t -> ('a -> 'b) -> 'b t
+  val (>>=) : 'a t -> ('a -> 'b t) -> 'b t
+end