(** * Theorems about State effects *)
(* begin hide *)
Program
Setoid
Morphisms
RelationClasses.
Basics.Basics
Basics.Category
Basics.CategoryKleisli
Basics.Monad
Core.ITreeDefinition
Core.KTree
Core.KTreeFacts
Eq.Eq
Eq.UpToTaus
Indexed.Sum
Interp.Interp
Interp.InterpFacts
Interp.RecursionFacts
Events.State.
Open Scope itree_scope.
(* end hide *)
Definition _interp_state {E F S R}
(f : E ~> stateT S (itree F)) (ot : itreeF E R _)
: stateT S (itree F) R := fun s =>
match ot with
| RetF r => Ret (s, r)
| TauF t => Tau (interp_state f t s)
| VisF e k => f _ e s >>= (fun sx => Tau (interp_state f (k (snd sx)) (fst sx)))
end.
Instance eq_itree_interp_state {E F S R} (h : E ~> Monads.stateT S (itree F)) :
Proper (eq_itree eq ==> eq ==> eq_itree eq)
(@interp_state _ _ _ _ _ _ h R).

Lemma interp_state_trigger {E F : Type -> Type} {R S : Type}
(e : E R) (f : E ~> Monads.stateT S (itree F)) (s : S)
: (interp_state f (ITree.trigger e) s) ≅ (f _ e s >>= fun x => Tau (Ret x)).