Module Type StateMonad.
Parameter state : forall (S X : Type), Type.
Definition State (S X : Type) := S -> state S X.
Parameter ret : forall {S X : Type}, X -> State S X.
Parameter bind : forall {S X Y}, State S X -> (X -> State S Y) -> State S Y.
Parameter get : forall {S}, State S S.
Parameter put : forall {S}, S -> State S unit.
End StateMonad.
Module Type RAM (M : StateMonad).
Parameter K : Type.
Parameter V : Type.
(* Inner implementation of RAM (TODO move or something) *)
Parameter S : Type.
(* Well-formedness over inner implementation (TODO move or remove from interface if possible) *)
Parameter well_formed : S -> Prop.
(* Read and write operations *)
Parameter read : K -> M.State S V.
Parameter write : K -> V -> M.State S unit.
Parameter equiv : forall {X},
M.State S X -> M.State S X -> Prop.

(* VI *)
Axiom write_commute : forall (k1 k2 : K) (v1 v2 : V),
k1 <> k2 ->
equiv
(M.bind (write k1 v1) (fun _ =>
write k2 v2))
(M.bind (write k2 v2) (fun _ =>
write k1 v1)).