src/HOL/Hoare/hoare.ML
author nipkow
Tue Mar 11 15:04:24 2003 +0100 (2003-03-11)
changeset 13857 11d7c5a8dbb7
parent 13737 e564c3d2d174
child 15531 08c8dad8e399
permissions -rw-r--r--
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(*  Title:      HOL/Hoare/Hoare.ML
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    ID:         $Id$
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    Author:     Leonor Prensa Nieto & Tobias Nipkow
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    Copyright   1998 TUM
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Derivation of the proof rules and, most importantly, the VCG tactic.
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*)
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val SkipRule = thm"SkipRule";
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val BasicRule = thm"BasicRule";
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val SeqRule = thm"SeqRule";
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val CondRule = thm"CondRule";
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val WhileRule = thm"WhileRule";
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(*** The tactics ***)
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(*****************************************************************************)
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(** The function Mset makes the theorem                                     **)
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(** "?Mset <= {(x1,...,xn). ?P (x1,...,xn)} ==> ?Mset <= {s. ?P s}",        **)
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(** where (x1,...,xn) are the variables of the particular program we are    **)
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(** working on at the moment of the call                                    **)
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(*****************************************************************************)
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local open HOLogic in
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(** maps (%x1 ... xn. t) to [x1,...,xn] **)
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fun abs2list (Const ("split",_) $ (Abs(x,T,t))) = Free (x, T)::abs2list t
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  | abs2list (Abs(x,T,t)) = [Free (x, T)]
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  | abs2list _ = [];
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(** maps {(x1,...,xn). t} to [x1,...,xn] **)
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fun mk_vars (Const ("Collect",_) $ T) = abs2list T
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  | mk_vars _ = [];
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(** abstraction of body over a tuple formed from a list of free variables. 
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Types are also built **)
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fun mk_abstupleC []     body = absfree ("x", unitT, body)
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  | mk_abstupleC (v::w) body = let val (n,T) = dest_Free v
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                               in if w=[] then absfree (n, T, body)
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        else let val z  = mk_abstupleC w body;
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                 val T2 = case z of Abs(_,T,_) => T
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                        | Const (_, Type (_,[_, Type (_,[T,_])])) $ _ => T;
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       in Const ("split", (T --> T2 --> boolT) --> mk_prodT (T,T2) --> boolT) 
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          $ absfree (n, T, z) end end;
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(** maps [x1,...,xn] to (x1,...,xn) and types**)
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fun mk_bodyC []      = HOLogic.unit
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  | mk_bodyC (x::xs) = if xs=[] then x 
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               else let val (n, T) = dest_Free x ;
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                        val z = mk_bodyC xs;
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                        val T2 = case z of Free(_, T) => T
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                                         | Const ("Pair", Type ("fun", [_, Type
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                                            ("fun", [_, T])])) $ _ $ _ => T;
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                 in Const ("Pair", [T, T2] ---> mk_prodT (T, T2)) $ x $ z end;
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fun dest_Goal (Const ("Goal", _) $ P) = P;
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(** maps a goal of the form:
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        1. [| P |] ==> VARS x1 ... xn {._.} _ {._.} or to [x1,...,xn]**) 
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fun get_vars thm = let  val c = dest_Goal (concl_of (thm));
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                        val d = Logic.strip_assums_concl c;
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                        val Const _ $ pre $ _ $ _ = dest_Trueprop d;
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      in mk_vars pre end;
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(** Makes Collect with type **)
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fun mk_CollectC trm = let val T as Type ("fun",[t,_]) = fastype_of trm 
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                      in Collect_const t $ trm end;
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fun inclt ty = Const ("op <=", [ty,ty] ---> boolT);
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(** Makes "Mset <= t" **)
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fun Mset_incl t = let val MsetT = fastype_of t 
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                 in mk_Trueprop ((inclt MsetT) $ Free ("Mset", MsetT) $ t) end;
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fun Mset thm = let val vars = get_vars(thm);
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                   val varsT = fastype_of (mk_bodyC vars);
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                   val big_Collect = mk_CollectC (mk_abstupleC vars 
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                         (Free ("P",varsT --> boolT) $ mk_bodyC vars));
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                   val small_Collect = mk_CollectC (Abs("x",varsT,
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                           Free ("P",varsT --> boolT) $ Bound 0));
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                   val impl = implies $ (Mset_incl big_Collect) $ 
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                                          (Mset_incl small_Collect);
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   in Tactic.prove (Thm.sign_of_thm thm) ["Mset", "P"] [] impl (K (CLASET' blast_tac 1)) end;
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end;
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(*****************************************************************************)
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(** Simplifying:                                                            **)
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(** Some useful lemmata, lists and simplification tactics to control which  **)
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(** theorems are used to simplify at each moment, so that the original      **)
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(** input does not suffer any unexpected transformation                     **)
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(*****************************************************************************)
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Goal "-(Collect b) = {x. ~(b x)}";
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by (Fast_tac 1);
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qed "Compl_Collect";
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(**Simp_tacs**)
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val before_set2pred_simp_tac =
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  (simp_tac (HOL_basic_ss addsimps [Collect_conj_eq RS sym,Compl_Collect]));
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val split_simp_tac = (simp_tac (HOL_basic_ss addsimps [split_conv]));
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(*****************************************************************************)
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(** set2pred transforms sets inclusion into predicates implication,         **)
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(** maintaining the original variable names.                                **)
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(** Ex. "{x. x=0} <= {x. x <= 1}" -set2pred-> "x=0 --> x <= 1"              **)
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(** Subgoals containing intersections (A Int B) or complement sets (-A)     **)
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(** are first simplified by "before_set2pred_simp_tac", that returns only   **)
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(** subgoals of the form "{x. P x} <= {x. Q x}", which are easily           **)
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(** transformed.                                                            **)
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(** This transformation may solve very easy subgoals due to a ligth         **)
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(** simplification done by (split_all_tac)                                  **)
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(*****************************************************************************)
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fun set2pred i thm = let fun mk_string [] = ""
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                           | mk_string (x::xs) = x^" "^mk_string xs;
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                         val vars=get_vars(thm);
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                         val var_string = mk_string (map (fst o dest_Free) vars);
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      in ((before_set2pred_simp_tac i) THEN_MAYBE
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          (EVERY [rtac subsetI i, 
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                  rtac CollectI i,
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                  dtac CollectD i,
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                  (TRY(split_all_tac i)) THEN_MAYBE
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                  ((rename_tac var_string i) THEN
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                   (full_simp_tac (HOL_basic_ss addsimps [split_conv]) i)) ])) thm
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      end;
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(*****************************************************************************)
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(** BasicSimpTac is called to simplify all verification conditions. It does **)
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(** a light simplification by applying "mem_Collect_eq", then it calls      **)
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(** MaxSimpTac, which solves subgoals of the form "A <= A",                 **)
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(** and transforms any other into predicates, applying then                 **)
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(** the tactic chosen by the user, which may solve the subgoal completely.  **)
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(*****************************************************************************)
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fun MaxSimpTac tac = FIRST'[rtac subset_refl, set2pred THEN_MAYBE' tac];
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fun BasicSimpTac tac =
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  simp_tac
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    (HOL_basic_ss addsimps [mem_Collect_eq,split_conv] addsimprocs [record_simproc])
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  THEN_MAYBE' MaxSimpTac tac;
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(** HoareRuleTac **)
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fun WlpTac Mlem tac i =
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  rtac SeqRule i THEN  HoareRuleTac Mlem tac false (i+1)
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and HoareRuleTac Mlem tac pre_cond i st = st |>
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        (*abstraction over st prevents looping*)
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    ( (WlpTac Mlem tac i THEN HoareRuleTac Mlem tac pre_cond i)
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      ORELSE
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      (FIRST[rtac SkipRule i,
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             EVERY[rtac BasicRule i,
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                   rtac Mlem i,
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                   split_simp_tac i],
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             EVERY[rtac CondRule i,
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                   HoareRuleTac Mlem tac false (i+2),
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                   HoareRuleTac Mlem tac false (i+1)],
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             EVERY[rtac WhileRule i,
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                   BasicSimpTac tac (i+2),
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                   HoareRuleTac Mlem tac true (i+1)] ] 
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       THEN (if pre_cond then (BasicSimpTac tac i) else (rtac subset_refl i)) ));
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(** tac:(int -> tactic) is the tactic the user chooses to solve or simplify **)
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(** the final verification conditions                                       **)
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fun hoare_tac tac i thm =
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  let val Mlem = Mset(thm)
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  in SELECT_GOAL(EVERY[HoareRuleTac Mlem tac true 1]) i thm end;