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(** {1 A certified WP calculus} *)

(** {2 A simple imperative language with expressions, syntax and semantics} *)

theory ImpExpr

use import int.Int
use import int.MinMax
use import bool.Bool
use export list.List
use map.Map as IdMap

(** types and values *)

type datatype = TYunit | TYint | TYbool
type value = Vvoid | Vint int | Vbool bool

(** terms and formulas *)

type operator = Oplus | Ominus | Omult | Ole

(* TODO: introduce two distinct
   types mident and ident *)
(** ident for mutable variable*)
type mident

(** ident for imutable variable*)
type ident = {| ident_index : int |}

constant result : ident

(** Terms *)
type term_node =
  | Tvalue value
  | Tvar ident
  | Tderef mident
  | Tbin term operator term

with term = {| term_node : term_node;
               term_maxvar : int;
             |}

predicate var_occurs_in_term (x:ident) (t:term) =
  match t with
  | {| term_node = Tvalue _ |} -> false
  | {| term_node = Tvar i |} -> x=i
  | {| term_node = Tderef _ |} -> false
  | {| term_node = Tbin t1 _ t2 |} -> var_occurs_in_term x t1 \/ var_occurs_in_term x t2
  end

predicate term_inv (t:term) =
  forall x:ident. var_occurs_in_term x t -> x.ident_index <= t.term_maxvar

function mk_tvalue (v:value) : term =
   {| term_node = Tvalue v; term_maxvar = -1 |}

lemma mk_tvalue_inv :
   forall v:value. term_inv (mk_tvalue v)

function mk_tvar (i:ident) : term =
   {| term_node = Tvar i; term_maxvar = i.ident_index |}

lemma mk_tvar_inv :
   forall i:ident. term_inv (mk_tvar i)

function mk_tderef (r:mident) : term =
   {| term_node = Tderef r; term_maxvar = -1 |}

lemma mk_tderef_inv :
   forall r:mident. term_inv (mk_tderef r)

function mk_tbin (t1:term) (o:operator) (t2:term) : term =
   {| term_node = Tbin t1 o t2;
      term_maxvar = max t1.term_maxvar t2.term_maxvar |}

lemma mk_tbin_inv :
   forall t1 t2:term, o:operator. term_inv t1 /\ term_inv t2 ->
     term_inv (mk_tbin t1 o t2)


(** Formulas *)
type fmla =
  | Fterm term
  | Fand fmla fmla
  | Fnot fmla
  | Fimplies fmla fmla
  | Flet ident term fmla         (* let id = term in fmla *)
  | Fforall ident datatype fmla  (* forall id : ty, fmla *)

(** Expressions *)
type expr =
  | Evalue value
  | Ebin expr operator expr
  | Evar ident
  | Ederef mident
  | Eassign mident expr
  | Eseq expr expr
  | Elet ident expr expr
  | Eif expr expr expr
  | Eassert fmla
  | Ewhile expr fmla expr  (* while cond invariant inv body *)

(** Typing *)

function type_value (v:value) : datatype =
    match v with
      | Vvoid  -> TYunit
      | Vint int ->  TYint
      | Vbool bool -> TYbool
end

inductive type_operator (op:operator) (ty1 ty2 ty: datatype) =
      | Type_plus : type_operator Oplus TYint TYint TYint
      | Type_minus : type_operator Ominus TYint TYint TYint
      | Type_mult : type_operator Omult TYint TYint TYint
      | Type_le : type_operator Ole TYint TYint TYbool

type type_stack = list (ident, datatype)  (* map local immutable variables to their type *)
function get_vartype (i:ident) (pi:type_stack) : datatype =
  match pi with
  | Nil -> TYunit
  | Cons (x,ty) r -> if x=i then ty else get_vartype i r
  end

type type_env = IdMap.map mident datatype  (* map global mutable variables to their type *)
function get_reftype (i:mident) (e:type_env) : datatype = IdMap.get e i

inductive type_term type_env type_stack term datatype =
  | Type_value :
      forall sigma: type_env, pi:type_stack, v:value, m:int.
	type_term sigma pi {| term_node = Tvalue v; term_maxvar = m |} (type_value v)
  | Type_var :
      forall sigma: type_env, pi:type_stack, v: ident, m:int, ty:datatype.
        (get_vartype v pi = ty) ->
        type_term sigma pi {| term_node = Tvar v ; term_maxvar = m |} ty
  | Type_deref :
      forall sigma: type_env, pi:type_stack, v: mident, m:int, ty:datatype.
        (get_reftype v sigma = ty) ->
        type_term sigma pi {| term_node = Tderef v; term_maxvar = m |} ty
  | Type_bin :
      forall sigma: type_env, pi:type_stack, t1 t2 : term, op:operator,
        m:int, ty1 ty2 ty:datatype.
        type_term sigma pi t1 ty1 ->
	type_term sigma pi t2 ty2 ->
	type_operator op ty1 ty2 ty ->
        type_term sigma pi {| term_node = Tbin t1 op t2; term_maxvar = m |} ty

inductive type_fmla type_env type_stack fmla =
  | Type_term :
      forall sigma: type_env, pi:type_stack, t:term.
	type_term sigma pi t TYbool ->
	type_fmla sigma pi (Fterm t)
  | Type_conj :
      forall sigma: type_env, pi:type_stack, f1 f2:fmla.
	type_fmla sigma pi f1 ->
        type_fmla sigma pi f2 ->
        type_fmla sigma pi (Fand f1 f2)
  | Type_neg :
      forall sigma: type_env, pi:type_stack, f:fmla.
	type_fmla sigma pi f ->
        type_fmla sigma pi (Fnot f)
  | Type_implies :
      forall sigma: type_env, pi:type_stack, f1 f2:fmla.
	type_fmla sigma pi f1 ->
        type_fmla sigma pi f2 ->
        type_fmla sigma pi (Fimplies f1 f2)
  | Type_let :
      forall sigma: type_env, pi:type_stack, x:ident, t:term, f:fmla, ty:datatype.
	type_term sigma pi t ty ->
        type_fmla sigma (Cons (x,ty) pi) f ->
        type_fmla sigma pi (Flet x t f)
  | Type_forall1 :
      forall sigma: type_env, pi:type_stack, x:ident, f:fmla.
        type_fmla sigma (Cons (x,TYint) pi) f ->
  	type_fmla sigma pi (Fforall x TYint f)
  | Type_forall2 :
      forall sigma: type_env, pi:type_stack, x:ident, f:fmla.
        type_fmla sigma (Cons (x,TYbool) pi) f ->
  	type_fmla sigma pi (Fforall x TYbool f)
  | Type_forall3:
      forall sigma: type_env, pi:type_stack, x:ident, f:fmla.
        type_fmla sigma (Cons (x,TYunit) pi) f ->
  	type_fmla sigma pi (Fforall x TYunit f)

inductive type_expr type_env type_stack expr datatype =
  | Type_evalue :
      forall sigma: type_env, pi:type_stack, v:value.
	type_expr sigma pi (Evalue v) (type_value v)
  | Type_evar   :
      forall sigma: type_env, pi:type_stack, v:ident, ty:datatype.
        (get_vartype v pi = ty) -> type_expr sigma pi (Evar v) ty
  | Type_ederef :
      forall sigma: type_env, pi:type_stack, v:mident, ty:datatype.
        (get_reftype v sigma = ty) -> type_expr sigma pi (Ederef v) ty
  | Type_ebin   :
      forall sigma: type_env, pi:type_stack, e1 e2:expr, op:operator, ty1 ty2 ty:datatype.
        type_expr sigma pi e1 ty1 ->
	type_expr sigma pi e2 ty2 ->
	type_operator op ty1 ty2 ty -> type_expr sigma pi (Ebin e1 op e2) ty
  | Type_eseq :
      forall sigma: type_env, pi:type_stack, e1 e2:expr, op:operator, ty:datatype.
        type_expr sigma pi e1 TYunit ->
	type_expr sigma pi e2 ty ->
	type_expr sigma pi (Eseq e1 e2) ty
  | Type_eassigns :
      forall sigma: type_env, pi:type_stack, x:mident, e:expr, ty:datatype.
	(get_reftype x sigma = ty) ->
        type_expr sigma pi e ty ->
        type_expr sigma pi (Eassign x e) TYunit
  | Type_elet :
      forall sigma: type_env, pi:type_stack, x:ident, e1 e2:expr, ty1 ty2 ty:datatype.
	type_expr sigma pi e1 ty1 ->
        type_expr sigma (Cons (x,ty2) pi) e2 ty2 ->
	type_expr sigma pi (Elet x e1 e2) ty2
  | Type_eif :
      forall sigma: type_env, pi:type_stack, e1 e2 e3:expr, ty:datatype.
	type_expr sigma pi e1 TYbool ->
	type_expr sigma pi e2 ty ->
	type_expr sigma pi e3 ty ->
    	type_expr sigma pi (Eif e1 e2 e3) ty
  | Type_eassert :
      forall sigma: type_env, pi:type_stack, p:fmla, ty:datatype.
	type_fmla sigma pi p ->
    	type_expr sigma pi (Eassert p) TYbool
  | Type_ewhile :
      forall sigma: type_env, pi:type_stack, guard body:expr, inv:fmla, ty:datatype.
	type_fmla sigma pi inv ->
        type_expr sigma pi guard TYbool ->
        type_expr sigma pi body TYunit ->
        type_expr sigma pi (Ewhile guard inv body) TYunit

(** Operational semantic *)
type env = IdMap.map mident value  (* map global mutable variables to their value *)
function get_env (i:mident) (e:env) : value = IdMap.get e i

type stack = list (ident, value)  (* map local immutable variables to their value *)
function get_stack (i:ident) (pi:stack) : value =
  match pi with
  | Nil -> Vvoid
  | Cons (x,v) r -> if x=i then v else get_stack i r
  end

lemma get_stack_eq:
  forall x:ident, v:value, r:stack.
    get_stack x (Cons (x,v) r) = v

lemma get_stack_neq:
  forall x i:ident, v:value, r:stack.
    x <> i -> get_stack i (Cons (x,v) r) = get_stack i r

(** semantics of formulas *)

function eval_bin (x:value) (op:operator) (y:value) : value =
  match x,y with
  | Vint x,Vint y ->
     match op with
     | Oplus -> Vint (x+y)
     | Ominus -> Vint (x-y)
     | Omult -> Vint (x*y)
     | Ole -> Vbool (if x <= y then True else False)
     end
  | _,_ -> Vvoid
  end

function eval_term (sigma:env) (pi:stack) (t:term) : value =
  match t with
  | {| term_node = Tvalue v |} -> v
  | {| term_node = Tvar id |} -> get_stack id pi
  | {| term_node = Tderef id |} -> get_env id sigma
  | {| term_node = Tbin t1 op t2 |} ->
     eval_bin (eval_term sigma pi t1) op (eval_term sigma pi t2)
  end

predicate eval_fmla (sigma:env) (pi:stack) (f:fmla) =
  match f with
  | Fterm t -> eval_term sigma pi t = Vbool True
  | Fand f1 f2 -> eval_fmla sigma pi f1 /\ eval_fmla sigma pi f2
  | Fnot f -> not (eval_fmla sigma pi f)
  | Fimplies f1 f2 -> eval_fmla sigma pi f1 -> eval_fmla sigma pi f2
  | Flet x t f ->
      eval_fmla sigma (Cons (x,eval_term sigma pi t) pi) f
  | Fforall x TYint f ->
     forall n:int. eval_fmla sigma (Cons (x,Vint n) pi) f
  | Fforall x TYbool f ->
     forall b:bool. eval_fmla sigma (Cons (x,Vbool b) pi) f
  | Fforall x TYunit f ->  eval_fmla sigma (Cons (x,Vvoid) pi) f
  end

(** substitution of a reference [r] by a logic variable [v]
   warning: proper behavior only guaranted if [v] is "fresh",
   i.e index(v) > term_maxvar(t) *)

function msubst_term (t:term) (r:mident) (v:ident) : term =
  match t with
  | {| term_node = Tvalue _ | Tvar _ |} -> t
  | {| term_node = Tderef x |} -> if r = x then mk_tvar v else t
  | {| term_node = Tbin t1 op t2 |} ->
      mk_tbin (msubst_term t1 r v) op (msubst_term t2 r v) 
  end

function subst_term (t:term) (r:ident) (v:ident) : term =
  match t with
  | {| term_node = Tvalue _ | Tderef _ |} -> t
  | {| term_node = Tvar x |} ->
      if r = x then mk_tvar v else t
  | {| term_node = Tbin t1 op t2 |} ->
     mk_tbin (subst_term t1 r v) op (subst_term t2 r v)
  end

(** [fresh_in_term id t] is true when [id] does not occur in [t] *)
predicate fresh_in_term (id:ident) (t:term) =
  id.ident_index > t.term_maxvar

lemma eval_msubst_term:
  forall sigma:env, pi:stack, e:term, x:mident, v:ident.
    fresh_in_term v e ->
    eval_term sigma pi (msubst_term e x v) =
    eval_term (IdMap.set sigma x (get_stack v pi)) pi e

lemma eval_subst_term:
  forall sigma:env, pi:stack, e:term, x:ident, v:ident.
    fresh_in_term v e ->
    eval_term sigma pi (subst_term e x v) =
    eval_term sigma (Cons (x, (get_stack v pi)) pi) e

lemma eval_term_change_free :
  forall t:term, sigma:env, pi:stack, id:ident, v:value.
    fresh_in_term id t ->
    eval_term sigma (Cons (id,v) pi) t = eval_term sigma pi t

predicate fresh_in_fmla (id:ident) (f:fmla) =
  match f with
  | Fterm e -> fresh_in_term id e
  | Fand f1 f2   | Fimplies f1 f2 ->
      fresh_in_fmla id f1 /\ fresh_in_fmla id f2
  | Fnot f -> fresh_in_fmla id f
  | Flet y t f -> id <> y /\ fresh_in_term id t /\ fresh_in_fmla id f
  | Fforall y ty f -> id <> y /\ fresh_in_fmla id f
  end

function subst (f:fmla) (x:ident) (v:ident) : fmla =
  match f with
  | Fterm e -> Fterm (subst_term e x v)
  | Fand f1 f2 -> Fand (subst f1 x v) (subst f2 x v)
  | Fnot f -> Fnot (subst f x v)
  | Fimplies f1 f2 -> Fimplies (subst f1 x v) (subst f2 x v)
  | Flet y t f -> Flet y (subst_term t x v) (subst f x v)
  | Fforall y ty f -> Fforall y ty (subst f x v)
  end

function msubst (f:fmla) (x:mident) (v:ident) : fmla =
  match f with
  | Fterm e -> Fterm (msubst_term e x v)
  | Fand f1 f2 -> Fand (msubst f1 x v) (msubst f2 x v)
  | Fnot f -> Fnot (msubst f x v)
  | Fimplies f1 f2 -> Fimplies (msubst f1 x v) (msubst f2 x v)
  | Flet y t f -> Flet y (msubst_term t x v) (msubst f x v)
  | Fforall y ty f -> Fforall y ty (msubst f x v)
  end

lemma subst_fresh :
  forall f:fmla, x:ident, v:ident.
   fresh_in_fmla x f -> subst f x v = f

lemma let_subst:
    forall t:term, f:fmla, x id':ident, id :mident.
    msubst (Flet x t f) id id' = Flet x (msubst_term t id id') (msubst f id id')

lemma eval_msubst:
  forall f:fmla, sigma:env, pi:stack, x:mident, v:ident.
    fresh_in_fmla v f ->
    (eval_fmla sigma pi (msubst f x v) <->
     eval_fmla (IdMap.set sigma x (get_stack v pi)) pi f)

lemma eval_subst:
  forall f:fmla, sigma:env, pi:stack, x:ident, v:ident.
    fresh_in_fmla v f ->
    (eval_fmla sigma pi (subst f x v) <->
     eval_fmla sigma (Cons(x, (get_stack v pi)) pi) f)

lemma eval_swap:
  forall f:fmla, sigma:env, pi:stack, id1 id2:ident, v1 v2:value.
    id1 <> id2 ->
    (eval_fmla sigma (Cons (id1,v1) (Cons (id2,v2) pi)) f <->
    eval_fmla sigma (Cons (id2,v2) (Cons (id1,v1) pi)) f)

lemma eval_same_var:
  forall f:fmla, sigma:env, pi:stack, id:ident, v1 v2:value.
    eval_fmla sigma (Cons (id,v1) (Cons (id,v2) pi)) f <->
    eval_fmla sigma (Cons (id,v1) pi) f

lemma eval_change_free :
  forall f:fmla, sigma:env, pi:stack, id:ident, v:value.
    fresh_in_fmla id f ->
    (eval_fmla sigma (Cons (id,v) pi) f <-> eval_fmla sigma pi f)


  (** [valid_fmla f] is true when [f] is valid in any environment *)
  predicate valid_fmla (p:fmla) = forall sigma:env, pi:stack. eval_fmla sigma pi p

(** let id' = t in f[id <- id'] <=> let id = t in f*)
lemma let_equiv :
  forall id:ident, id':ident, t:term, f:fmla.
    forall sigma:env, pi:stack.
      fresh_in_fmla id' f ->
	(eval_fmla sigma pi (Flet id' t (subst f id id'))
	 -> eval_fmla sigma pi (Flet id t f))

lemma let_equiv2 :
  forall id:ident, id':ident, t:term, f:fmla.
    forall sigma:env, pi:stack.
      fresh_in_fmla id' f ->
	eval_fmla sigma pi (Flet id' t (subst f id id'))
	 -> eval_fmla sigma pi (Flet id t f)

lemma let_implies :
  forall id:ident, t:term, p q:fmla.
    valid_fmla (Fimplies p q) ->
    valid_fmla (Fimplies (Flet id t p) (Flet id t q))

predicate fresh_in_expr (id:ident) (e:expr) =
  match e with
  | Evalue _ -> true
  | Eseq e1 e2
  | Ebin e1 _ e2 -> fresh_in_expr id e1 /\ fresh_in_expr id e2
  | Evar v -> id <> v
  | Ederef _ -> true
  | Eassign _ e -> fresh_in_expr id e
  | Elet v e1 e2 -> id <>v /\ fresh_in_expr id e1 /\ fresh_in_expr id e2
  | Eif e1 e2 e3 -> fresh_in_expr id e1 /\ fresh_in_expr id e2 /\ fresh_in_expr id e3
  | Eassert f -> fresh_in_fmla id f
  | Ewhile cond inv body -> fresh_in_expr id cond /\ fresh_in_fmla id inv /\ fresh_in_expr id body
  end


constant void : expr = Evalue Vvoid

(** small-steps semantics for expressions *)

inductive one_step env stack expr env stack expr =

  | one_step_var:
      forall sigma:env, pi:stack, v:ident.
        one_step sigma pi (Evar v) sigma pi (Evalue (get_stack v pi))

  | one_step_deref:
      forall sigma:env, pi:stack, v:mident.
        one_step sigma pi (Ederef v) sigma pi (Evalue (get_env v sigma))

  | one_step_bin_ctxt1:
      forall sigma sigma':env, pi pi':stack, op:operator,
        e1 e1' e2:expr.
        one_step sigma pi e1 sigma' pi' e1' ->
          one_step sigma pi (Ebin e1 op e2) sigma' pi' (Ebin e1' op e2)

  | one_step_bin_ctxt2:
      forall sigma sigma':env, pi pi':stack, op:operator, v1:value, e2 e2':expr.
        one_step sigma pi e2 sigma' pi' e2' ->
          one_step sigma pi (Ebin (Evalue v1) op e2) sigma' pi' (Ebin (Evalue v1) op e2')

  | one_step_bin_value:
      forall sigma sigma':env, pi pi':stack, op:operator, v1 v2:value.
        one_step sigma pi (Ebin (Evalue v1) op (Evalue v2)) sigma' pi' (Evalue (eval_bin v1 op v2))

  | one_step_assign_ctxt:
      forall sigma sigma':env, pi pi':stack, x:mident, e e':expr.
        one_step sigma pi e sigma' pi' e' ->
        one_step sigma pi (Eassign x e)
                 sigma' pi' (Eassign x e')

  | one_step_assign_value:
      forall sigma:env, pi:stack, x:mident, v:value, e:term.
        one_step sigma pi (Eassign x (Evalue v))
                 (IdMap.set sigma x v) pi void

  | one_step_seq_ctxt:
      forall sigma sigma':env, pi pi':stack, e1 e1' e2:expr.
        one_step sigma pi e1 sigma' pi' e1' ->
          one_step sigma pi (Eseq e1 e2) sigma' pi' (Eseq e1' e2)

  | one_step_seq_value:
      forall sigma:env, pi:stack, id:ident, e:expr.
        one_step sigma pi (Eseq void e) sigma pi e

  | one_step_let_ctxt:
      forall sigma sigma':env, pi pi':stack, id:ident, e1 e1' e2:expr.
        one_step sigma pi e1 sigma' pi' e1' ->
          one_step sigma pi (Elet id e1 e2) sigma' pi' (Elet id e1' e2)

  | one_step_let_value:
      forall sigma:env, pi:stack, id:ident, v:value, e:expr.
        one_step sigma pi (Elet id (Evalue v) e) sigma (Cons (id,v) pi) e

  | one_step_if_ctxt:
      forall sigma sigma':env, pi pi':stack, id:ident, e1 e1' e2 e3:expr.
        one_step sigma pi e1 sigma' pi' e1' ->
          one_step sigma pi (Eif e1 e2 e3) sigma' pi' (Eif e1' e2 e3)

  | one_step_if_true:
      forall sigma:env, pi:stack, e:term, e1 e2:expr.
        one_step sigma pi (Eif (Evalue (Vbool True)) e1 e2) sigma pi e1

  | one_step_if_false:
      forall sigma:env, pi:stack, e:term, e1 e2:expr.
        one_step sigma pi (Eif (Evalue (Vbool False)) e1 e2) sigma pi e2

  | one_step_assert:
      forall sigma:env, pi:stack, f:fmla.
        (* blocking semantics *)
        eval_fmla sigma pi f ->
          one_step sigma pi (Eassert f) sigma pi void

  | one_step_while:
      forall sigma:env, pi:stack, cond:expr, inv:fmla, body:expr.
        (* blocking semantics *)
        eval_fmla sigma pi inv ->
        one_step sigma pi (Ewhile cond inv body) sigma pi
        (Eif cond (Eseq body (Ewhile cond inv body)) void)

 (** many steps of execution *)

 inductive many_steps env stack expr env stack expr int =
   | many_steps_refl:
     forall sigma:env, pi:stack, e:expr. many_steps sigma pi e sigma pi e 0
   | many_steps_trans:
     forall sigma1 sigma2 sigma3:env, pi1 pi2 pi3:stack, e1 e2 e3:expr, n:int.
       one_step sigma1 pi1 e1 sigma2 pi2 e2 ->
       many_steps sigma2 pi2 e2 sigma3 pi3 e3 n ->
       many_steps sigma1 pi1 e1 sigma3 pi3 e3 (n+1)

  lemma steps_non_neg:
    forall sigma1 sigma2:env, pi1 pi2:stack, e1 e2:expr, n:int.
      many_steps sigma1 pi1 e1 sigma2 pi2 e2 n -> n >= 0

  lemma many_steps_seq:
    forall sigma1 sigma3:env, pi1 pi3:stack, e1 e2:expr, n:int.
      many_steps sigma1 pi1 (Eseq e1 e2) sigma3 pi3 void n ->
      exists sigma2:env, pi2:stack, n1 n2:int.
        many_steps sigma1 pi1 e1 sigma2 pi2 void n1 /\
        many_steps sigma2 pi2 e2 sigma3 pi3 void n2 /\
        n = 1 + n1 + n2

  lemma many_steps_let:
    forall sigma1 sigma3:env, pi1 pi3:stack, id:ident, e1 e2:expr, v2:value, n:int.
      many_steps sigma1 pi1 (Elet id e1 e2) sigma3 pi3 (Evalue v2) n ->
      exists sigma2:env, pi2:stack, v1:value, n1 n2:int.
        many_steps sigma1 pi1 e1 sigma2 pi2 (Evalue v1) n1 /\
        many_steps sigma2 (Cons (id,v1) pi2) e2 sigma3 pi3 (Evalue v2) n2 /\
        n = 1 + n1 + n2

 lemma one_step_change_free :
  forall e e':expr, sigma sigma':env, pi pi':stack, id:ident, v:value.
    fresh_in_expr id e ->
    one_step sigma (Cons (id,v) pi) e sigma' pi' e' ->
    one_step sigma pi e sigma' pi' e'



(** {3 Hoare triples} *)

(** partial correctness *)
predicate valid_triple (p:fmla) (e:expr) (q:fmla) =
    forall sigma:env, pi:stack. eval_fmla sigma pi p ->
      forall sigma':env, pi':stack, v:value, n:int.
        many_steps sigma pi e sigma' pi' (Evalue v) n ->
          eval_fmla sigma' (Cons (result,v) pi') q

(*** total correctness *)
predicate total_valid_triple (p:fmla) (e:expr) (q:fmla) =
    forall sigma:env, pi:stack. eval_fmla sigma pi p ->
      exists sigma':env, pi':stack, v:value, n:int.
        many_steps sigma pi e sigma' pi' (Evalue v) n /\
        eval_fmla sigma' (Cons (result,v) pi') q

end


theory TestSemantics

use import ImpExpr

function my_sigma : env = IdMap.const (Vint 0)
constant x : ident
constant y : mident

function my_pi : stack = Cons (x, Vint 42) Nil

goal Test13 :
  eval_term my_sigma my_pi (mk_tvalue (Vint 13)) = Vint 13

goal Test13expr :
  many_steps my_sigma my_pi (Evalue (Vint 13)) my_sigma my_pi (Evalue (Vint 13)) 0

goal Test42 :
  eval_term my_sigma my_pi (mk_tvar x) = Vint 42

goal Test42expr :
  many_steps my_sigma my_pi (Evar x) my_sigma my_pi (Evalue (Vint 42)) 1

goal Test0 :
  eval_term my_sigma my_pi (mk_tderef y) = Vint 0

goal Test0expr :
  many_steps my_sigma my_pi (Ederef y) my_sigma my_pi (Evalue (Vint 0)) 1

goal Test55 :
  eval_term my_sigma my_pi (mk_tbin (mk_tvar x) Oplus (mk_tvalue (Vint 13))) = Vint 55

goal Test55expr :
  many_steps my_sigma my_pi (Ebin (Evar x) Oplus (Evalue (Vint 13))) my_sigma my_pi (Evalue (Vint 55)) 2

goal Ass42 :
  forall sigma':env, pi':stack.
    one_step my_sigma my_pi (Eassign y (Evalue (Vint 42))) sigma' pi' void ->
      IdMap.get sigma' y = Vint 42

goal If42 :
    forall sigma1 sigma2:env, pi1 pi2:stack, e:expr.
      one_step my_sigma my_pi
        (Eif (Ebin (Ederef y) Ole (Evalue (Vint 10)))
             (Eassign y (Evalue (Vint 13)))
             (Eassign y (Evalue (Vint 42))))
        sigma1 pi1 e ->
      one_step sigma1 pi1 e sigma2 pi2 void ->
        IdMap.get sigma2 y = Vint 13

end

(** {2 Hoare logic} *)

theory HoareLogic

use import ImpExpr


(** Hoare logic rules (partial correctness) *)

lemma consequence_rule:
  forall p p' q q':fmla, e:expr.
  valid_fmla (Fimplies p' p) ->
  valid_triple p e q ->
  valid_fmla (Fimplies q q') ->
  valid_triple p' e q'

lemma value_rule:
  forall q:fmla, v:value. fresh_in_fmla result q ->
  valid_triple q (Evalue v) q

lemma assign_rule:
  forall p q:fmla, x:mident, e:expr.
  valid_triple p e (msubst q x result) ->
  valid_triple p (Eassign x e) q

lemma seq_rule:
  forall p q r:fmla, e1 e2:expr.
  valid_triple p e1 r /\ valid_triple r e2 q ->
  valid_triple p (Eseq e1 e2) q

lemma let_rule:
  forall p q r:fmla, id:ident, e1 e2:expr.
  id <> result -> fresh_in_fmla id r ->
  valid_triple p e1 r /\ valid_triple (Flet result (mk_tvar id) r) e2 q ->
  valid_triple p (Elet id e1 e2) q

(*
lemma if_rule:
  forall e:expr, p q:fmla, i1 i2:expr.
  valid_triple (Fand p (Fterm e)) i1 q /\
  valid_triple (Fand p (Fnot (Fterm e))) i2 q ->
  valid_triple p (Eif e e1 e2) q
*)

lemma assert_rule:
  forall f p:fmla. valid_fmla (Fimplies p f) ->
  valid_triple p (Eassert f) p

lemma assert_rule_ext:
  forall f p:fmla.
  valid_triple (Fimplies f p) (Eassert f) p

(*
lemma while_rule:
  forall e:term, inv:fmla, i:expr.
  valid_triple (Fand (Fterm e) inv) i inv ->
  valid_triple inv (Swhile e inv i) (Fand (Fnot (Fterm e)) inv)

lemma while_rule_ext:
  forall e:term, inv inv':fmla, i:expr.
  valid_fmla (Fimplies inv' inv) ->
  valid_triple (Fand (Fterm e) inv') i inv' ->
  valid_triple inv' (Swhile e inv i) (Fand (Fnot (Fterm e)) inv')
*)

(*** frame rule ? *)

end

theory Simpl_tautology

  predicate p
  predicate q

  lemma simpl_tautology :
    (p -> q) <-> (p /\ q <-> p)

end

(** {2 WP calculus} *)

theory WP

use import ImpExpr
use import bool.Bool

use set.Set

(** [assigns sigma W sigma'] is true when the only differences between
    [sigma] and [sigma'] are the value of references in [W] *)

predicate assigns (sigma:env) (a:Set.set mident) (sigma':env) =
  forall i:mident. not (Set.mem i a) ->
    IdMap.get sigma i = IdMap.get sigma' i

lemma assigns_refl:
  forall sigma:env, a:Set.set mident. assigns sigma a sigma

lemma assigns_trans:
  forall sigma1 sigma2 sigma3:env, a:Set.set mident.
    assigns sigma1 a sigma2 /\ assigns sigma2 a sigma3 ->
    assigns sigma1 a sigma3

lemma assigns_union_left:
  forall sigma sigma':env, s1 s2:Set.set mident.
    assigns sigma s1 sigma' -> assigns sigma (Set.union s1 s2) sigma'

lemma assigns_union_right:
  forall sigma sigma':env, s1 s2:Set.set mident.
    assigns sigma s2 sigma' -> assigns sigma (Set.union s1 s2) sigma'

(** [expr_writes e W] is true when the only references modified by [e] are in [W] *)
predicate expr_writes (e:expr) (w:Set.set mident) =
  match e with
  | Evalue _ | Evar _ | Ederef _ | Eassert _ -> true
  | Ebin e1 _ e2 -> expr_writes e1 w /\ expr_writes e2 w
  | Eassign id _ -> Set.mem id w
  | Eseq e1 e2 -> expr_writes e1 w /\ expr_writes e2 w
  | Elet id e1 e2 -> expr_writes e1 w /\ expr_writes e2 w
  | Eif e1 e2 e3 -> expr_writes e1 w /\ expr_writes e2 w /\ expr_writes e3 w
  | Ewhile cond _ body -> expr_writes cond w /\ expr_writes body w
  end

  function fresh_from (f:fmla) (e:expr) : ident

  axiom fresh_from_fmla: forall e:expr, f:fmla.
     fresh_in_fmla (fresh_from f e) f

  axiom fresh_from_expr: forall e:expr, f:fmla.
     fresh_in_expr (fresh_from f e) e

  function abstract_effects (e:expr) (f:fmla) : fmla

  function wp (e:expr) (q:fmla) : fmla =
    match e with
    | Evalue v ->
        (* let result = v in q *)
        Flet result (mk_tvalue v) q
    | Evar v -> Flet result (mk_tvar v) q
    | Ederef x -> Flet result (mk_tderef x) q
    | Eassert f ->
        (* asymmetric and *)
        Fand f (Fimplies f (Flet result (mk_tvalue Vvoid) q))
    | Eseq e1 e2 -> wp e1 (wp e2 q)
    | Elet id e1 e2 -> wp e1 (Flet id (mk_tvar result) (wp e2 q))
    | Ebin e1 op e2 ->
       let t1 = fresh_from q e in
       let t2 = fresh_from (Fand (Fterm (mk_tvar t1)) q) e in
       let q' = Flet result (mk_tbin (mk_tvar t1) op (mk_tvar t2)) q in
       let f = wp e2 (Flet t2 (mk_tvar result) q') in
       wp e1 (Flet t1 (mk_tvar result) f)
       (* let wp_op = subst q (Tvar result) (Tbin (Tvar t1) op (Tvar t2)) in *)
       (* let wp2 = (subst (wp e2 wp_op) t2 (Tvar result)) in *)
       (* (subst (wp e1 wp2) t1 (Tvar result)) *)
    | Eassign x e ->
        let id = fresh_from q e in
        let q' = Flet result (mk_tvalue Vvoid) q in
        wp e (Flet id (mk_tvar result) (msubst q' x id))
    | Eif e1 e2 e3 ->
        let f =
          Fand (Fimplies (Fterm (mk_tvar result)) (wp e2 q))
            (Fimplies (Fnot (Fterm (mk_tvar result))) (wp e3 q))
        in
        wp e1 f
    | Ewhile cond inv body ->
        Fand inv
          (abstract_effects body
            (wp cond
             (Fand
              (Fimplies (Fand (Fterm (mk_tvar result)) inv) (wp body inv))
              (Fimplies (Fand (Fnot (Fterm (mk_tvar result))) inv) q))))

    end


  lemma result_always_fresh_in_wp:
     forall e:expr, q:fmla. fresh_in_fmla result (wp e q)

  (* lemma wp_subst: *)
  (*   forall e:expr, q:fmla, id :mident, id':ident. *)
  (*   fresh_in_expr id e -> *)
  (*     subst (wp e q) id id' = wp e (subst q id id') *)

  lemma distrib_conj:
    forall sigma:env, pi:stack, e:expr, p q:fmla.
     eval_fmla sigma pi (wp e (Fand p q)) <->
       (eval_fmla sigma pi (wp e p)) /\
       (eval_fmla sigma pi (wp e q))

  lemma monotonicity:
    forall e:expr, p q:fmla.
      valid_fmla (Fimplies p q)
     ->	valid_fmla (Fimplies (wp e p) (wp e q) )

  lemma wp_reduction:
    forall sigma sigma':env, pi pi':stack, e e':expr.
    one_step sigma pi e sigma' pi' e' ->
    forall q:fmla.
      eval_fmla sigma pi (wp e q) ->
      eval_fmla sigma' pi' (wp e' q)

  predicate is_value (e:expr) =
    match e with
    | Evalue _ -> true
    | _ -> false
    end

  lemma decide_value :
    forall e:expr. not (is_value e) \/ exists v:value. e = Evalue v

  lemma bool_value:
    forall v:value, sigmat: type_env, pit:type_stack.
      type_expr sigmat pit (Evalue v) TYbool ->
          (v = Vbool False) \/ (v = Vbool True)

  lemma unit_value:
    forall v:value, sigmat: type_env, pit:type_stack.
      type_expr sigmat pit (Evalue v) TYunit -> v = Vvoid

  lemma progress:
    forall e:expr, sigma:env, pi:stack, sigmat: type_env, pit: type_stack, ty: datatype, q:fmla.
      type_expr sigmat pit e ty ->
      type_fmla sigmat (Cons(result, ty) pit) q ->
    eval_fmla sigma pi (wp e q) -> not is_value e ->
    exists sigma':env, pi':stack, e':expr.
      one_step sigma pi e sigma' pi' e'

end


(***
Local Variables:
compile-command: "why3ide blocking_semantics3.mlw"
End:
*)