src/HOL/Hoare/Hoare_Logic.thy

Hoare syntax: standard abstraction syntax admits source positions;
re-unified some clones (!);

(*  Title:      HOL/Hoare/Hoare_Logic.thy
    Author:     Leonor Prensa Nieto & Tobias Nipkow
    Copyright   1998 TUM

Sugared semantic embedding of Hoare logic.
Strictly speaking a shallow embedding (as implemented by Norbert Galm
following Mike Gordon) would suffice. Maybe the datatype com comes in useful
later.
*)

theory Hoare_Logic
imports Main
uses ("hoare_tac.ML")
begin

types
    'a bexp = "'a set"
    'a assn = "'a set"

datatype
 'a com = Basic "'a \<Rightarrow> 'a"
   | Seq "'a com" "'a com"               ("(_;/ _)"      [61,60] 60)
   | Cond "'a bexp" "'a com" "'a com"    ("(1IF _/ THEN _ / ELSE _/ FI)"  [0,0,0] 61)
   | While "'a bexp" "'a assn" "'a com"  ("(1WHILE _/ INV {_} //DO _ /OD)"  [0,0,0] 61)

abbreviation annskip ("SKIP") where "SKIP == Basic id"

types 'a sem = "'a => 'a => bool"

inductive Sem :: "'a com \<Rightarrow> 'a sem"
where
  "Sem (Basic f) s (f s)"
| "Sem c1 s s'' \<Longrightarrow> Sem c2 s'' s' \<Longrightarrow> Sem (c1;c2) s s'"
| "s \<in> b \<Longrightarrow> Sem c1 s s' \<Longrightarrow> Sem (IF b THEN c1 ELSE c2 FI) s s'"
| "s \<notin> b \<Longrightarrow> Sem c2 s s' \<Longrightarrow> Sem (IF b THEN c1 ELSE c2 FI) s s'"
| "s \<notin> b \<Longrightarrow> Sem (While b x c) s s"
| "s \<in> b \<Longrightarrow> Sem c s s'' \<Longrightarrow> Sem (While b x c) s'' s' \<Longrightarrow>
   Sem (While b x c) s s'"

inductive_cases [elim!]:
  "Sem (Basic f) s s'" "Sem (c1;c2) s s'"
  "Sem (IF b THEN c1 ELSE c2 FI) s s'"

definition Valid :: "'a bexp \<Rightarrow> 'a com \<Rightarrow> 'a bexp \<Rightarrow> bool"
  where "Valid p c q \<longleftrightarrow> (!s s'. Sem c s s' --> s : p --> s' : q)"



(** parse translations **)

syntax
  "_assign" :: "idt => 'b => 'a com"  ("(2_ :=/ _)" [70, 65] 61)

syntax
 "_hoare_vars" :: "[idts, 'a assn,'a com,'a assn] => bool"
                 ("VARS _// {_} // _ // {_}" [0,0,55,0] 50)
syntax ("" output)
 "_hoare"      :: "['a assn,'a com,'a assn] => bool"
                 ("{_} // _ // {_}" [0,55,0] 50)

parse_translation {*
  let
    fun mk_abstuple [x] body = Syntax.abs_tr [x, body]
      | mk_abstuple (x :: xs) body =
          Syntax.const @{const_syntax prod_case} $ Syntax.abs_tr [x, mk_abstuple xs body];

    fun mk_fbody x e [y] = if Syntax.eq_idt (x, y) then e else y
      | mk_fbody x e (y :: xs) =
          Syntax.const @{const_syntax Pair} $
            (if Syntax.eq_idt (x, y) then e else y) $ mk_fbody x e xs;

    fun mk_fexp x e xs = mk_abstuple xs (mk_fbody x e xs);

    (* bexp_tr & assn_tr *)
    (*all meta-variables for bexp except for TRUE are translated as if they
      were boolean expressions*)

    fun bexp_tr (Const ("TRUE", _)) xs = Syntax.const "TRUE"   (* FIXME !? *)
      | bexp_tr b xs = Syntax.const @{const_syntax Collect} $ mk_abstuple xs b;

    fun assn_tr r xs = Syntax.const @{const_syntax Collect} $ mk_abstuple xs r;

    (* com_tr *)

    fun com_tr (Const (@{syntax_const "_assign"}, _) $ x $ e) xs =
          Syntax.const @{const_syntax Basic} $ mk_fexp x e xs
      | com_tr (Const (@{const_syntax Basic},_) $ f) xs = Syntax.const @{const_syntax Basic} $ f
      | com_tr (Const (@{const_syntax Seq},_) $ c1 $ c2) xs =
          Syntax.const @{const_syntax Seq} $ com_tr c1 xs $ com_tr c2 xs
      | com_tr (Const (@{const_syntax Cond},_) $ b $ c1 $ c2) xs =
          Syntax.const @{const_syntax Cond} $ bexp_tr b xs $ com_tr c1 xs $ com_tr c2 xs
      | com_tr (Const (@{const_syntax While},_) $ b $ I $ c) xs =
          Syntax.const @{const_syntax While} $ bexp_tr b xs $ assn_tr I xs $ com_tr c xs
      | com_tr t _ = t;

    fun vars_tr (Const (@{syntax_const "_idts"}, _) $ idt $ vars) = idt :: vars_tr vars
      | vars_tr t = [t];

    fun hoare_vars_tr [vars, pre, prg, post] =
          let val xs = vars_tr vars
          in Syntax.const @{const_syntax Valid} $
             assn_tr pre xs $ com_tr prg xs $ assn_tr post xs
          end
      | hoare_vars_tr ts = raise TERM ("hoare_vars_tr", ts);

  in [(@{syntax_const "_hoare_vars"}, hoare_vars_tr)] end
*}


(*****************************************************************************)

(*** print translations ***)
ML{*
fun dest_abstuple (Const (@{const_syntax prod_case},_) $ (Abs(v,_, body))) =
                            subst_bound (Syntax.free v, dest_abstuple body)
  | dest_abstuple (Abs(v,_, body)) = subst_bound (Syntax.free v, body)
  | dest_abstuple trm = trm;

fun abs2list (Const (@{const_syntax prod_case},_) $ (Abs(x,T,t))) = Free (x, T)::abs2list t
  | abs2list (Abs(x,T,t)) = [Free (x, T)]
  | abs2list _ = [];

fun mk_ts (Const (@{const_syntax prod_case},_) $ (Abs(x,_,t))) = mk_ts t
  | mk_ts (Abs(x,_,t)) = mk_ts t
  | mk_ts (Const (@{const_syntax Pair},_) $ a $ b) = a::(mk_ts b)
  | mk_ts t = [t];

fun mk_vts (Const (@{const_syntax prod_case},_) $ (Abs(x,_,t))) =
           ((Syntax.free x)::(abs2list t), mk_ts t)
  | mk_vts (Abs(x,_,t)) = ([Syntax.free x], [t])
  | mk_vts t = raise Match;

fun find_ch [] i xs = (false, (Syntax.free "not_ch", Syntax.free "not_ch"))
  | find_ch ((v,t)::vts) i xs =
      if t = Bound i then find_ch vts (i-1) xs
      else (true, (v, subst_bounds (xs, t)));

fun is_f (Const (@{const_syntax prod_case},_) $ (Abs(x,_,t))) = true
  | is_f (Abs(x,_,t)) = true
  | is_f t = false;
*}

(* assn_tr' & bexp_tr'*)
ML{*
fun assn_tr' (Const (@{const_syntax Collect},_) $ T) = dest_abstuple T
  | assn_tr' (Const (@{const_syntax inter}, _) $
        (Const (@{const_syntax Collect},_) $ T1) $ (Const (@{const_syntax Collect},_) $ T2)) =
      Syntax.const @{const_syntax inter} $ dest_abstuple T1 $ dest_abstuple T2
  | assn_tr' t = t;

fun bexp_tr' (Const (@{const_syntax Collect},_) $ T) = dest_abstuple T
  | bexp_tr' t = t;
*}

(*com_tr' *)
ML{*
fun mk_assign f =
  let val (vs, ts) = mk_vts f;
      val (ch, which) = find_ch (vs~~ts) ((length vs)-1) (rev vs)
  in
    if ch then Syntax.const @{syntax_const "_assign"} $ fst which $ snd which
    else Syntax.const @{const_syntax annskip}
  end;

fun com_tr' (Const (@{const_syntax Basic},_) $ f) =
      if is_f f then mk_assign f
      else Syntax.const @{const_syntax Basic} $ f
  | com_tr' (Const (@{const_syntax Seq},_) $ c1 $ c2) =
      Syntax.const @{const_syntax Seq} $ com_tr' c1 $ com_tr' c2
  | com_tr' (Const (@{const_syntax Cond},_) $ b $ c1 $ c2) =
      Syntax.const @{const_syntax Cond} $ bexp_tr' b $ com_tr' c1 $ com_tr' c2
  | com_tr' (Const (@{const_syntax While},_) $ b $ I $ c) =
      Syntax.const @{const_syntax While} $ bexp_tr' b $ assn_tr' I $ com_tr' c
  | com_tr' t = t;

fun spec_tr' [p, c, q] =
  Syntax.const @{syntax_const "_hoare"} $ assn_tr' p $ com_tr' c $ assn_tr' q
*}

print_translation {* [(@{const_syntax Valid}, spec_tr')] *}

lemma SkipRule: "p \<subseteq> q \<Longrightarrow> Valid p (Basic id) q"
by (auto simp:Valid_def)

lemma BasicRule: "p \<subseteq> {s. f s \<in> q} \<Longrightarrow> Valid p (Basic f) q"
by (auto simp:Valid_def)

lemma SeqRule: "Valid P c1 Q \<Longrightarrow> Valid Q c2 R \<Longrightarrow> Valid P (c1;c2) R"
by (auto simp:Valid_def)

lemma CondRule:
 "p \<subseteq> {s. (s \<in> b \<longrightarrow> s \<in> w) \<and> (s \<notin> b \<longrightarrow> s \<in> w')}
  \<Longrightarrow> Valid w c1 q \<Longrightarrow> Valid w' c2 q \<Longrightarrow> Valid p (Cond b c1 c2) q"
by (auto simp:Valid_def)

lemma While_aux:
  assumes "Sem (WHILE b INV {i} DO c OD) s s'"
  shows "\<forall>s s'. Sem c s s' \<longrightarrow> s \<in> I \<and> s \<in> b \<longrightarrow> s' \<in> I \<Longrightarrow>
    s \<in> I \<Longrightarrow> s' \<in> I \<and> s' \<notin> b"
  using assms
  by (induct "WHILE b INV {i} DO c OD" s s') auto

lemma WhileRule:
 "p \<subseteq> i \<Longrightarrow> Valid (i \<inter> b) c i \<Longrightarrow> i \<inter> (-b) \<subseteq> q \<Longrightarrow> Valid p (While b i c) q"
apply (clarsimp simp:Valid_def)
apply(drule While_aux)
  apply assumption
 apply blast
apply blast
done


lemma Compl_Collect: "-(Collect b) = {x. ~(b x)}"
  by blast

lemmas AbortRule = SkipRule  -- "dummy version"
use "hoare_tac.ML"

method_setup vcg = {*
  Scan.succeed (fn ctxt => SIMPLE_METHOD' (hoare_tac ctxt (K all_tac))) *}
  "verification condition generator"

method_setup vcg_simp = {*
  Scan.succeed (fn ctxt =>
    SIMPLE_METHOD' (hoare_tac ctxt (asm_full_simp_tac (simpset_of ctxt)))) *}
  "verification condition generator plus simplification"

end