module type Monad = sig
  type 'a t

  val return : 'a -> 'a t
  val bind   : 'a t -> ('a -> 'b t) -> 'b t
end

module type FullMonad = sig
  type 'a t

  val return : 'a -> 'a t
  val bind   : 'a t -> ('a -> 'b t) -> 'b t
  val (>>=)  : 'a t -> ('a -> 'b t) -> 'b t
  val (let*) : 'a t -> ('a -> 'b t) -> 'b t
  val join   : 'a t t -> 'a t
end

module Expand (M : Monad) = struct
  include M

  let (>>=)  = M.bind
  let (let*) = M.bind
  let join m = M.bind m (fun m -> m)
end