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+(** Impure monad for interface with impure code
+
+*)
+
+Require Export Program.
+Require Export ImpConfig.
+
+(* Theory: bind + embed => dbind
+
+Program Definition dbind {A B} (k1: t A) (k2: forall (a:A), (mayRet k1 a) -> t B) : t B
+ := bind (mk_annot k1) (fun a => k2 a _).
+
+Lemma mayRet_dbind: forall (A B:Type) k1 k2 (b:B),
+ mayRet (dbind k1 k2) b -> exists a:A, exists H: (mayRet k1 a), mayRet (k2 a H) b.
+Proof.
+ intros A B k1 k2 b H; decompose [ex and] (mayRet_bind _ _ _ _ _ H).
+ eapply ex_intro.
+ eapply ex_intro.
+ eauto.
+Qed.
+
+*)
+
+Definition wlp {A:Type} (k: t A) (P: A -> Prop): Prop
+ := forall a, mayRet k a -> P a.
+
+(* Notations *)
+
+(* Print Grammar constr. *)
+
+Module Notations.
+
+ Bind Scope impure_scope with t.
+ Delimit Scope impure_scope with impure.
+
+ Notation "?? A" := (t A) (at level 0, A at level 95): impure_scope.
+
+ Notation "k '~~>' a" := (mayRet k a) (at level 75, no associativity): impure_scope.
+
+ Notation "'RET' a" := (ret a) (at level 0): impure_scope.
+
+ Notation "'DO' x '<~' k1 ';;' k2" := (bind k1 (fun x => k2))
+ (at level 55, k1 at level 53, x at level 99, right associativity): impure_scope.
+
+ Notation "k1 ';;' k2" := (bind k1 (fun _ => k2))
+ (at level 55, right associativity): impure_scope.
+
+ Notation "'WHEN' k '~>' a 'THEN' R" := (wlp k (fun a => R))
+ (at level 73, R at level 100, right associativity): impure_scope.
+
+ Notation "'ASSERT' P" := (ret (A:=P) _) (at level 0, only parsing): impure_scope.
+
+End Notations.
+
+Import Notations.
+Local Open Scope impure.
+
+Goal ((?? list nat * ??nat -> nat) = ((?? ((list nat) * ?? nat) -> nat)))%type.
+Proof.
+ apply refl_equal.
+Qed.
+
+
+(* wlp lemmas for tactics *)
+
+Lemma wlp_unfold A (k:??A)(P: A -> Prop):
+ (forall a, k ~~> a -> P a)
+ -> wlp k P.
+Proof.
+ auto.
+Qed.
+
+Lemma wlp_monotone A (k:?? A) (P1 P2: A -> Prop):
+ wlp k P1
+ -> (forall a, k ~~> a -> P1 a -> P2 a)
+ -> wlp k P2.
+Proof.
+ unfold wlp; eauto.
+Qed.
+
+Lemma wlp_forall A B (k:?? A) (P: B -> A -> Prop):
+ (forall x, wlp k (P x))
+ -> wlp k (fun a => forall x, P x a).
+Proof.
+ unfold wlp; auto.
+Qed.
+
+Lemma wlp_ret A (P: A -> Prop) a:
+ P a -> wlp (ret a) P.
+Proof.
+ unfold wlp.
+ intros H b H0.
+ rewrite <- (mayRet_ret _ a b H0).
+ auto.
+Qed.
+
+Lemma wlp_bind A B (k1:??A) (k2: A -> ??B) (P: B -> Prop):
+ wlp k1 (fun a => wlp (k2 a) P) -> wlp (bind k1 k2) P.
+Proof.
+ unfold wlp.
+ intros H a H0.
+ case (mayRet_bind _ _ _ _ _ H0); clear H0.
+ intuition eauto.
+Qed.
+
+Lemma wlp_ifbool A (cond: bool) (k1 k2: ?? A) (P: A -> Prop):
+ (cond=true -> wlp k1 P) -> (cond=false -> wlp k2 P) -> wlp (if cond then k1 else k2) P.
+Proof.
+ destruct cond; auto.
+Qed.
+
+Lemma wlp_letprod (A B C: Type) (p: A*B) (k: A -> B -> ??C) (P: C -> Prop):
+ (wlp (k (fst p) (snd p)) P)
+ -> (wlp (let (x,y):=p in (k x y)) P).
+Proof.
+ destruct p; simpl; auto.
+Qed.
+
+Lemma wlp_sum (A B C: Type) (x: A+B) (k1: A -> ??C) (k2: B -> ??C) (P: C -> Prop):
+ (forall a, x=inl a -> wlp (k1 a) P) ->
+ (forall b, x=inr b -> wlp (k2 b) P) ->
+ (wlp (match x with inl a => k1 a | inr b => k2 b end) P).
+Proof.
+ destruct x; simpl; auto.
+Qed.
+
+Lemma wlp_sumbool (A B:Prop) (C: Type) (x: {A}+{B}) (k1: A -> ??C) (k2: B -> ??C) (P: C -> Prop):
+ (forall a, x=left a -> wlp (k1 a) P) ->
+ (forall b, x=right b -> wlp (k2 b) P) ->
+ (wlp (match x with left a => k1 a | right b => k2 b end) P).
+Proof.
+ destruct x; simpl; auto.
+Qed.
+
+Lemma wlp_option (A B: Type) (x: option A) (k1: A -> ??B) (k2: ??B) (P: B -> Prop):
+ (forall a, x=Some a -> wlp (k1 a) P) ->
+ (x=None -> wlp k2 P) ->
+ (wlp (match x with Some a => k1 a | None => k2 end) P).
+Proof.
+ destruct x; simpl; auto.
+Qed.
+
+(* Tactics
+
+MAIN tactics:
+ - xtsimplify "base": simplification using from hints in "base" database (in particular "wlp" lemmas).
+ - xtstep "base": only one step of simplification.
+
+For good performance, it is recommanded to have several databases.
+
+*)
+
+Ltac introcomp :=
+ let a:= fresh "exta" in
+ let H:= fresh "Hexta" in
+ intros a H.
+
+(* decompose the current wlp goal using "introduction" rules *)
+Ltac wlp_decompose :=
+ apply wlp_ret
+ || apply wlp_bind
+ || apply wlp_ifbool
+ || apply wlp_letprod
+ || apply wlp_sum
+ || apply wlp_sumbool
+ || apply wlp_option
+ .
+
+(* this tactic simplifies the current "wlp" goal using any hint found via tactic "hint". *)
+Ltac apply_wlp_hint hint :=
+ eapply wlp_monotone;
+ [ hint; fail | idtac ] ;
+ simpl; introcomp.
+
+(* one step of wlp_xsimplify
+*)
+Ltac wlp_step hint :=
+ match goal with
+ | |- (wlp _ _) =>
+ wlp_decompose
+ || apply_wlp_hint hint
+ || (apply wlp_unfold; introcomp)
+ end.
+
+(* main general tactic
+WARNING: for the good behavior of "wlp_xsimplify", "hint" must at least perform a "eauto".
+
+Example of use:
+ wlp_xsimplify (intuition eauto with base).
+*)
+Ltac wlp_xsimplify hint :=
+ repeat (intros; subst; wlp_step hint; simpl; (tauto || hint)).
+
+Create HintDb wlp discriminated.
+
+Ltac wlp_simplify := wlp_xsimplify ltac:(intuition eauto with wlp). \ No newline at end of file