Source file state.ml

(* This file is part of 'travesty'.

   Copyright (c) 2018 by Matt Windsor

   Permission is hereby granted, free of charge, to any person obtaining a
   copy of this software and associated documentation files (the "Software"),
   to deal in the Software without restriction, including without limitation
   the rights to use, copy, modify, merge, publish, distribute, sublicense,
   and/or sell copies of the Software, and to permit persons to whom the
   Software is furnished to do so, subject to the following conditions:

   The above copyright notice and this permission notice shall be included in
   all copies or substantial portions of the Software.

   THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
   IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
   FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
   THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
   LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
   FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
   DEALINGS IN THE SOFTWARE. *)

open Base
open State_types

(* We implement all of the various monads and functors in terms of
   [State_transform] and the identity monad, for simplicity. This reflects
   the situation in Haskell, except that Haskell has curried type
   constructors and we have separate arity modules. *)

module M2 : S2 = State_transform.Make2 (Monad.Ident)

module To_S (M : S2) (B : Base.T) :
  S with type state = B.t and type 'a t = ('a, B.t) M.t = struct
  type state = B.t

  module M1 = struct
    type 'a t = ('a, state) M.t

    include Monad_exts.S2_to_S (M) (B)
  end

  include M1
  include Monad_exts.Extend (M1)

  include (
    M :
      Generic
        with type ('a, 's) t := 'a t
         and type 'a final := 'a
         and type 's state := state )
end

module Make (B : T) : S with type state = B.t = State_transform.Make (struct
  type t = B.t

  module Inner = Monad.Ident
end)