TFL/post.ML
author wenzelm
Mon Jun 19 22:06:36 2006 +0200 (2006-06-19)
changeset 19927 9286e99b2808
parent 19925 3f9341831812
child 20061 2b142bfb162a
permissions -rw-r--r--
refrain from reforming TFL -- back to previous revision;
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(*  Title:      TFL/post.ML
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    ID:         $Id$
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    Author:     Konrad Slind, Cambridge University Computer Laboratory
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    Copyright   1997  University of Cambridge
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Second part of main module (postprocessing of TFL definitions).
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*)
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signature TFL =
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sig
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  val trace: bool ref
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  val quiet_mode: bool ref
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  val message: string -> unit
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  val tgoalw: theory -> thm list -> thm list -> thm list
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  val tgoal: theory -> thm list -> thm list
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  val define_i: bool -> theory -> claset -> simpset -> thm list -> thm list -> xstring ->
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    term -> term list -> theory * {rules: (thm * int) list, induct: thm, tcs: term list}
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  val define: bool -> theory -> claset -> simpset -> thm list -> thm list -> xstring ->
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    string -> string list -> theory * {rules: (thm * int) list, induct: thm, tcs: term list}
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  val defer_i: theory -> thm list -> xstring -> term list -> theory * thm
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  val defer: theory -> thm list -> xstring -> string list -> theory * thm
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end;
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structure Tfl: TFL =
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struct
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structure S = USyntax
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(* messages *)
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val trace = Prim.trace
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val quiet_mode = ref false;
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fun message s = if ! quiet_mode then () else writeln s;
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(* misc *)
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(*---------------------------------------------------------------------------
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 * Extract termination goals so that they can be put it into a goalstack, or
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 * have a tactic directly applied to them.
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 *--------------------------------------------------------------------------*)
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fun termination_goals rules =
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    map (Type.freeze o HOLogic.dest_Trueprop)
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      (foldr (fn (th,A) => gen_union (op aconv) (prems_of th, A)) [] rules);
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(*---------------------------------------------------------------------------
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 * Finds the termination conditions in (highly massaged) definition and
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 * puts them into a goalstack.
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 *--------------------------------------------------------------------------*)
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fun tgoalw thy defs rules =
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  case termination_goals rules of
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      [] => error "tgoalw: no termination conditions to prove"
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    | L  => OldGoals.goalw_cterm defs
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              (Thm.cterm_of (Theory.sign_of thy)
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                        (HOLogic.mk_Trueprop(USyntax.list_mk_conj L)));
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fun tgoal thy = tgoalw thy [];
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(*---------------------------------------------------------------------------
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 * Three postprocessors are applied to the definition.  It
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 * attempts to prove wellfoundedness of the given relation, simplifies the
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 * non-proved termination conditions, and finally attempts to prove the
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 * simplified termination conditions.
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 *--------------------------------------------------------------------------*)
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fun std_postprocessor strict cs ss wfs =
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  Prim.postprocess strict
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   {wf_tac     = REPEAT (ares_tac wfs 1),
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    terminator = asm_simp_tac ss 1
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                 THEN TRY (silent_arith_tac 1 ORELSE
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                           fast_tac (cs addSDs [not0_implies_Suc] addss ss) 1),
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    simplifier = Rules.simpl_conv ss []};
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val concl = #2 o Rules.dest_thm;
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(*---------------------------------------------------------------------------
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 * Postprocess a definition made by "define". This is a separate stage of
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 * processing from the definition stage.
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 *---------------------------------------------------------------------------*)
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local
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structure R = Rules
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structure U = Utils
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(* The rest of these local definitions are for the tricky nested case *)
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val solved = not o can S.dest_eq o #2 o S.strip_forall o concl
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fun id_thm th =
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   let val {lhs,rhs} = S.dest_eq (#2 (S.strip_forall (#2 (R.dest_thm th))));
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   in lhs aconv rhs end
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   handle U.ERR _ => false;
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fun prover s = prove_goal HOL.thy s (fn _ => [fast_tac HOL_cs 1]);
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val P_imp_P_iff_True = prover "P --> (P= True)" RS mp;
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val P_imp_P_eq_True = P_imp_P_iff_True RS eq_reflection;
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fun mk_meta_eq r = case concl_of r of
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     Const("==",_)$_$_ => r
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  |   _ $(Const("op =",_)$_$_) => r RS eq_reflection
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  |   _ => r RS P_imp_P_eq_True
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(*Is this the best way to invoke the simplifier??*)
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fun rewrite L = rewrite_rule (map mk_meta_eq (List.filter(not o id_thm) L))
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fun join_assums th =
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  let val {sign,...} = rep_thm th
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      val tych = cterm_of sign
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      val {lhs,rhs} = S.dest_eq(#2 (S.strip_forall (concl th)))
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      val cntxtl = (#1 o S.strip_imp) lhs  (* cntxtl should = cntxtr *)
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      val cntxtr = (#1 o S.strip_imp) rhs  (* but union is solider *)
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      val cntxt = gen_union (op aconv) (cntxtl, cntxtr)
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  in
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    R.GEN_ALL
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      (R.DISCH_ALL
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         (rewrite (map (R.ASSUME o tych) cntxt) (R.SPEC_ALL th)))
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  end
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  val gen_all = S.gen_all
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in
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fun proof_stage strict cs ss wfs theory {f, R, rules, full_pats_TCs, TCs} =
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  let
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    val _ = message "Proving induction theorem ..."
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    val ind = Prim.mk_induction theory {fconst=f, R=R, SV=[], pat_TCs_list=full_pats_TCs}
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    val _ = message "Postprocessing ...";
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    val {rules, induction, nested_tcs} =
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      std_postprocessor strict cs ss wfs theory {rules=rules, induction=ind, TCs=TCs}
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  in
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  case nested_tcs
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  of [] => {induction=induction, rules=rules,tcs=[]}
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  | L  => let val dummy = message "Simplifying nested TCs ..."
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              val (solved,simplified,stubborn) =
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               fold_rev (fn th => fn (So,Si,St) =>
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                     if (id_thm th) then (So, Si, th::St) else
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                     if (solved th) then (th::So, Si, St)
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                     else (So, th::Si, St)) nested_tcs ([],[],[])
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              val simplified' = map join_assums simplified
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              val dummy = (Prim.trace_thms "solved =" solved;
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                           Prim.trace_thms "simplified' =" simplified')
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              val rewr = full_simplify (ss addsimps (solved @ simplified'));
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              val dummy = Prim.trace_thms "Simplifying the induction rule..."
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                                          [induction]
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              val induction' = rewr induction
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              val dummy = Prim.trace_thms "Simplifying the recursion rules..."
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                                          [rules]
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              val rules'     = rewr rules
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              val _ = message "... Postprocessing finished";
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          in
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          {induction = induction',
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               rules = rules',
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                 tcs = map (gen_all o S.rhs o #2 o S.strip_forall o concl)
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                           (simplified@stubborn)}
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          end
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  end;
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(*lcp: curry the predicate of the induction rule*)
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fun curry_rule rl =
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  SplitRule.split_rule_var (Term.head_of (HOLogic.dest_Trueprop (concl_of rl))) rl;
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(*lcp: put a theorem into Isabelle form, using meta-level connectives*)
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val meta_outer =
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  curry_rule o standard o
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  rule_by_tactic (REPEAT (FIRSTGOAL (resolve_tac [allI, impI, conjI] ORELSE' etac conjE)));
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(*Strip off the outer !P*)
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val spec'= read_instantiate [("x","P::?'b=>bool")] spec;
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fun tracing true _ = ()
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  | tracing false msg = writeln msg;
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fun simplify_defn strict thy cs ss congs wfs id pats def0 =
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   let val def = Thm.freezeT def0 RS meta_eq_to_obj_eq
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       val {theory,rules,rows,TCs,full_pats_TCs} =
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           Prim.post_definition congs (thy, (def,pats))
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       val {lhs=f,rhs} = S.dest_eq (concl def)
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       val (_,[R,_]) = S.strip_comb rhs
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       val dummy = Prim.trace_thms "congs =" congs
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       (*the next step has caused simplifier looping in some cases*)
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       val {induction, rules, tcs} =
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             proof_stage strict cs ss wfs theory
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               {f = f, R = R, rules = rules,
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                full_pats_TCs = full_pats_TCs,
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                TCs = TCs}
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       val rules' = map (standard o ObjectLogic.rulify_no_asm)
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                        (R.CONJUNCTS rules)
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         in  {induct = meta_outer (ObjectLogic.rulify_no_asm (induction RS spec')),
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        rules = ListPair.zip(rules', rows),
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        tcs = (termination_goals rules') @ tcs}
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   end
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  handle U.ERR {mesg,func,module} =>
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               error (mesg ^
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                      "\n    (In TFL function " ^ module ^ "." ^ func ^ ")");
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(* Derive the initial equations from the case-split rules to meet the
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users specification of the recursive function. 
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 Note: We don't do this if the wf conditions fail to be solved, as each
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case may have a different wf condition. We could group the conditions
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together and say that they must be true to solve the general case,
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but that would hide from the user which sub-case they were related
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to. Probably this is not important, and it would work fine, but, for now, I
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prefer leaving more fine-grain control to the user. 
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-- Lucas Dixon, Aug 2004 *)
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local
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  fun get_related_thms i = 
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      List.mapPartial ((fn (r,x) => if x = i then SOME r else NONE));
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  fun solve_eq (th, [], i) = 
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        error "derive_init_eqs: missing rules"
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    | solve_eq (th, [a], i) = [(a, i)]
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    | solve_eq (th, splitths as (_ :: _), i) = 
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      (writeln "Proving unsplit equation...";
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      [((standard o ObjectLogic.rulify_no_asm)
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          (CaseSplit.splitto splitths th), i)])
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      (* if there's an error, pretend nothing happened with this definition 
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         We should probably print something out so that the user knows...? *)
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      handle ERROR s => 
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             (warning ("recdef (solve_eq): " ^ s); map (fn x => (x,i)) splitths);
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in
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fun derive_init_eqs sgn rules eqs = 
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    let 
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      val eqths = map (Thm.trivial o (Thm.cterm_of sgn) o HOLogic.mk_Trueprop) 
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                      eqs
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      fun countlist l = 
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          (rev o snd o (Library.foldl (fn ((i,L), e) => (i + 1,(e,i) :: L)))) ((0,[]), l)
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    in
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      List.concat (map (fn (e,i) => solve_eq (e, (get_related_thms i rules), i))
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                (countlist eqths))
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    end;
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end;
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(*---------------------------------------------------------------------------
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 * Defining a function with an associated termination relation.
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 *---------------------------------------------------------------------------*)
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fun define_i strict thy cs ss congs wfs fid R eqs =
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  let val {functional,pats} = Prim.mk_functional thy eqs
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      val (thy, def) = Prim.wfrec_definition0 thy (Sign.base_name fid) R functional
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      val {induct, rules, tcs} = 
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          simplify_defn strict thy cs ss congs wfs fid pats def
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      val rules' = 
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          if strict then derive_init_eqs (Theory.sign_of thy) rules eqs
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          else rules
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  in (thy, {rules = rules', induct = induct, tcs = tcs}) end;
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fun define strict thy cs ss congs wfs fid R seqs =
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  define_i strict thy cs ss congs wfs fid (Sign.read_term thy R) (map (Sign.read_term thy) seqs)
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    handle U.ERR {mesg,...} => error mesg;
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(*---------------------------------------------------------------------------
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 *
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 *     Definitions with synthesized termination relation
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 *
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 *---------------------------------------------------------------------------*)
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fun func_of_cond_eqn tm =
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  #1 (S.strip_comb (#lhs (S.dest_eq (#2 (S.strip_forall (#2 (S.strip_imp tm)))))));
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fun defer_i thy congs fid eqs =
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 let val {rules,R,theory,full_pats_TCs,SV,...} =
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             Prim.lazyR_def thy (Sign.base_name fid) congs eqs
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     val f = func_of_cond_eqn (concl (R.CONJUNCT1 rules handle U.ERR _ => rules));
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     val dummy = message "Proving induction theorem ...";
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     val induction = Prim.mk_induction theory
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                        {fconst=f, R=R, SV=SV, pat_TCs_list=full_pats_TCs}
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 in (theory,
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     (*return the conjoined induction rule and recursion equations,
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       with assumptions remaining to discharge*)
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     standard (induction RS (rules RS conjI)))
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 end
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fun defer thy congs fid seqs =
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  defer_i thy congs fid (map (Sign.read_term thy) seqs)
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    handle U.ERR {mesg,...} => error mesg;
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end;
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end;