Source file monad_intf.ml

(*
 * Copyright (c) 2019-2021 Craig Ferguson <craig@tarides.com>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 *)

module type S = sig
  type 'a t

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

module type EXTENDED = sig
  include S

  module Syntax : sig
    val ( let* ) : 'a t -> ('a -> 'b t) -> 'b t
    val ( let+ ) : 'a t -> ('a -> 'b) -> 'b t
    val ( >>= ) : 'a t -> ('a -> 'b t) -> 'b t
    val ( >|= ) : 'a t -> ('a -> 'b) -> 'b t
  end

  module List : sig
    val fold_map_s :
      ('acc -> 'a -> ('acc * 'b) t) -> 'acc -> 'a list -> ('acc * 'b list) t
  end
end

module type Monad = sig
  module type S = S
  module type EXTENDED = EXTENDED

  module Identity : S with type 'a t = 'a
  module Extend (M : S) : EXTENDED with type 'a t = 'a M.t
end