(*  Title:      Pure/meta_simplifier.ML

     ID:         $Id$

     Author:     Tobias Nipkow and Stefan Berghofer

 Meta-level Simplification.

 *)

 signature BASIC_META_SIMPLIFIER =

 sig

   val trace_simp: bool ref

   val debug_simp: bool ref

   val simp_depth_limit: int ref

 end;

 signature META_SIMPLIFIER =

 sig

   include BASIC_META_SIMPLIFIER

   exception SIMPLIFIER of string * thm

   exception SIMPROC_FAIL of string * exn

   type meta_simpset

   val dest_mss          : meta_simpset ->

     {simps: thm list, congs: thm list, procs: (string * cterm list) list}

   val empty_mss         : meta_simpset

   val clear_mss         : meta_simpset -> meta_simpset

   val merge_mss         : meta_simpset * meta_simpset -> meta_simpset

   val add_simps         : meta_simpset * thm list -> meta_simpset

   val del_simps         : meta_simpset * thm list -> meta_simpset

   val mss_of            : thm list -> meta_simpset

   val add_congs         : meta_simpset * thm list -> meta_simpset

   val del_congs         : meta_simpset * thm list -> meta_simpset

   val add_simprocs      : meta_simpset *

     (string * cterm list * (Sign.sg -> thm list -> term -> thm option) * stamp) list

       -> meta_simpset

   val del_simprocs      : meta_simpset *

     (string * cterm list * (Sign.sg -> thm list -> term -> thm option) * stamp) list

       -> meta_simpset

   val add_prems         : meta_simpset * thm list -> meta_simpset

   val prems_of_mss      : meta_simpset -> thm list

   val set_mk_rews       : meta_simpset * (thm -> thm list) -> meta_simpset

   val set_mk_sym        : meta_simpset * (thm -> thm option) -> meta_simpset

   val set_mk_eq_True    : meta_simpset * (thm -> thm option) -> meta_simpset

   val get_mk_rews       : meta_simpset -> thm -> thm list

   val get_mk_sym        : meta_simpset -> thm -> thm option

   val get_mk_eq_True    : meta_simpset -> thm -> thm option

   val set_termless      : meta_simpset * (term * term -> bool) -> meta_simpset

   val rewrite_cterm: bool * bool * bool ->

     (meta_simpset -> thm -> thm option) -> meta_simpset -> cterm -> thm

   val rewrite_aux       : (meta_simpset -> thm -> thm option) -> bool -> thm list -> cterm -> thm

   val simplify_aux      : (meta_simpset -> thm -> thm option) -> bool -> thm list -> thm -> thm

   val rewrite_thm       : bool * bool * bool

                           -> (meta_simpset -> thm -> thm option)

                           -> meta_simpset -> thm -> thm

   val rewrite_goals_rule_aux: (meta_simpset -> thm -> thm option) -> thm list -> thm -> thm

   val rewrite_goal_rule : bool* bool * bool

                           -> (meta_simpset -> thm -> thm option)

                           -> meta_simpset -> int -> thm -> thm

   val rewrite_term: Sign.sg -> thm list -> (term -> term option) list -> term -> term

 end;

 structure MetaSimplifier : META_SIMPLIFIER =

 struct

 (** diagnostics **)

 exception SIMPLIFIER of string * thm;

 exception SIMPROC_FAIL of string * exn;

 val simp_depth = ref 0;

 val simp_depth_limit = ref 1000;

 local

 fun println a =

   tracing ((case ! simp_depth of 0 => "" | n => "[" ^ string_of_int n ^ "]") ^ a);

 fun prnt warn a = if warn then warning a else println a;

 fun prtm warn a sign t = prnt warn (a ^ "\n" ^ Sign.string_of_term sign t);

 fun prctm warn a t = prnt warn (a ^ "\n" ^ Display.string_of_cterm t);

 in

 fun prthm warn a = prctm warn a o Thm.cprop_of;

 val trace_simp = ref false;

 val debug_simp = ref false;

 fun trace warn a = if !trace_simp then prnt warn a else ();

 fun debug warn a = if !debug_simp then prnt warn a else ();

 fun trace_term warn a sign t = if !trace_simp then prtm warn a sign t else ();

 fun trace_cterm warn a t = if !trace_simp then prctm warn a t else ();

 fun debug_term warn a sign t = if !debug_simp then prtm warn a sign t else ();

 fun trace_thm a thm =

   let val {sign, prop, ...} = rep_thm thm

   in trace_term false a sign prop end;

 fun trace_named_thm a (thm, name) =

   trace_thm (a ^ (if name = "" then "" else " " ^ quote name) ^ ":") thm;

 end;

 (** meta simp sets **)

 (* basic components *)

 type rrule = {thm: thm, name: string, lhs: term, elhs: cterm, fo: bool, perm: bool};

 (* thm: the rewrite rule

    name: name of theorem from which rewrite rule was extracted

    lhs: the left-hand side

    elhs: the etac-contracted lhs.

    fo:  use first-order matching

    perm: the rewrite rule is permutative

 Remarks:

   - elhs is used for matching,

     lhs only for preservation of bound variable names.

   - fo is set iff

     either elhs is first-order (no Var is applied),

            in which case fo-matching is complete,

     or elhs is not a pattern,

        in which case there is nothing better to do.

 *)

 type cong = {thm: thm, lhs: cterm};

 type simproc =

  {name: string, proc: Sign.sg -> thm list -> term -> thm option, lhs: cterm, id: stamp};

 fun eq_rrule ({thm = thm1, ...}: rrule, {thm = thm2, ...}: rrule) =

   #prop (rep_thm thm1) aconv #prop (rep_thm thm2);

 fun eq_cong ({thm = thm1, ...}: cong, {thm = thm2, ...}: cong) =

   #prop (rep_thm thm1) aconv #prop (rep_thm thm2);

 fun eq_prem (thm1, thm2) =

   #prop (rep_thm thm1) aconv #prop (rep_thm thm2);

 fun eq_simproc ({id = s1, ...}:simproc, {id = s2, ...}:simproc) = (s1 = s2);

 fun mk_simproc (name, proc, lhs, id) =

   {name = name, proc = proc, lhs = lhs, id = id};

 (* datatype mss *)

 (*

   A "mss" contains data needed during conversion:

     rules: discrimination net of rewrite rules;

     congs: association list of congruence rules and

            a list of `weak' congruence constants.

            A congruence is `weak' if it avoids normalization of some argument.

     procs: discrimination net of simplification procedures

       (functions that prove rewrite rules on the fly);

     bounds: names of bound variables already used

       (for generating new names when rewriting under lambda abstractions);

     prems: current premises;

     mk_rews: mk: turns simplification thms into rewrite rules;

              mk_sym: turns == around; (needs Drule!)

              mk_eq_True: turns P into P == True - logic specific;

     termless: relation for ordered rewriting;

     depth: depth of conditional rewriting;

 *)

 datatype meta_simpset =

   Mss of {

     rules: rrule Net.net,

     congs: (string * cong) list * string list,

     procs: simproc Net.net,

     bounds: string list,

     prems: thm list,

     mk_rews: {mk: thm -> thm list,

               mk_sym: thm -> thm option,

               mk_eq_True: thm -> thm option},

     termless: term * term -> bool,

     depth: int};

 fun mk_mss (rules, congs, procs, bounds, prems, mk_rews, termless, depth) =

   Mss {rules = rules, congs = congs, procs = procs, bounds = bounds,

        prems=prems, mk_rews=mk_rews, termless=termless, depth=depth};

 fun upd_rules(Mss{rules,congs,procs,bounds,prems,mk_rews,termless,depth}, rules') =

   mk_mss(rules',congs,procs,bounds,prems,mk_rews,termless,depth);

 val empty_mss =

   let val mk_rews = {mk = K [], mk_sym = K None, mk_eq_True = K None}

   in mk_mss (Net.empty, ([], []), Net.empty, [], [], mk_rews, Term.termless, 0) end;

 fun clear_mss (Mss {mk_rews, termless, ...}) =

   mk_mss (Net.empty, ([], []), Net.empty, [], [], mk_rews, termless,0);

 fun incr_depth(Mss{rules,congs,procs,bounds,prems,mk_rews,termless,depth}) =

   let val depth1 = depth+1

   in if depth1 > !simp_depth_limit

      then (warning "simp_depth_limit exceeded - giving up"; None)

      else (if depth1 mod 10 = 0

            then warning("Simplification depth " ^ string_of_int depth1)

            else ();

            Some(mk_mss(rules,congs,procs,bounds,prems,mk_rews,termless,depth1))

           )

   end;

 (** simpset operations **)

 (* term variables *)

 val add_term_varnames = foldl_aterms (fn (xs, Var (x, _)) => ins_ix (x, xs) | (xs, _) => xs);

 fun term_varnames t = add_term_varnames ([], t);

 (* dest_mss *)

 fun dest_mss (Mss {rules, congs, procs, ...}) =

   {simps = map (fn (_, {thm, ...}) => thm) (Net.dest rules),

    congs = map (fn (_, {thm, ...}) => thm) (fst congs),

    procs =

      map (fn (_, {name, lhs, id, ...}) => ((name, lhs), id)) (Net.dest procs)

      |> partition_eq eq_snd

      |> map (fn ps => (#1 (#1 (hd ps)), map (#2 o #1) ps))

      |> Library.sort_wrt #1};

 (* merge_mss *)       (*NOTE: ignores mk_rews, termless and depth of 2nd mss*)

 fun merge_mss

  (Mss {rules = rules1, congs = (congs1,weak1), procs = procs1,

        bounds = bounds1, prems = prems1, mk_rews, termless, depth},

   Mss {rules = rules2, congs = (congs2,weak2), procs = procs2,

        bounds = bounds2, prems = prems2, ...}) =

       mk_mss

        (Net.merge (rules1, rules2, eq_rrule),

         (gen_merge_lists (eq_cong o pairself snd) congs1 congs2,

         merge_lists weak1 weak2),

         Net.merge (procs1, procs2, eq_simproc),

         merge_lists bounds1 bounds2,

         gen_merge_lists eq_prem prems1 prems2,

         mk_rews, termless, depth);

 (* add_simps *)

 fun mk_rrule2{thm, name, lhs, elhs, perm} =

   let val fo = Pattern.first_order (term_of elhs) orelse not(Pattern.pattern (term_of elhs))

   in {thm=thm, name=name, lhs=lhs, elhs=elhs, fo=fo, perm=perm} end

 fun insert_rrule quiet (mss as Mss {rules,...},

                  rrule as {thm,name,lhs,elhs,perm}) =

   (trace_named_thm "Adding rewrite rule" (thm, name);

    let val rrule2 as {elhs,...} = mk_rrule2 rrule

        val rules' = Net.insert_term ((term_of elhs, rrule2), rules, eq_rrule)

    in upd_rules(mss,rules') end

    handle Net.INSERT => if quiet then mss else

      (prthm true "Ignoring duplicate rewrite rule:" thm; mss));

 fun vperm (Var _, Var _) = true

   | vperm (Abs (_, _, s), Abs (_, _, t)) = vperm (s, t)

   | vperm (t1 $ t2, u1 $ u2) = vperm (t1, u1) andalso vperm (t2, u2)

   | vperm (t, u) = (t = u);

 fun var_perm (t, u) =

   vperm (t, u) andalso eq_set (term_varnames t, term_varnames u);

 (* FIXME: it seems that the conditions on extra variables are too liberal if

 prems are nonempty: does solving the prems really guarantee instantiation of

 all its Vars? Better: a dynamic check each time a rule is applied.

 *)

 fun rewrite_rule_extra_vars prems elhs erhs =

   not (term_varnames erhs subset foldl add_term_varnames (term_varnames elhs, prems))

   orelse

   not ((term_tvars erhs) subset

        (term_tvars elhs  union  List.concat(map term_tvars prems)));

 (*Simple test for looping rewrite rules and stupid orientations*)

 fun reorient sign prems lhs rhs =

    rewrite_rule_extra_vars prems lhs rhs

   orelse

    is_Var (head_of lhs)

   orelse

    (exists (apl (lhs, Logic.occs)) (rhs :: prems))

   orelse

    (null prems andalso

     Pattern.matches (Sign.tsig_of sign) (lhs, rhs))

     (*the condition "null prems" is necessary because conditional rewrites

       with extra variables in the conditions may terminate although

       the rhs is an instance of the lhs. Example: ?m < ?n ==> f(?n) == f(?m)*)

   orelse

    (is_Const lhs andalso not(is_Const rhs))

 fun decomp_simp thm =

   let val {sign, prop, ...} = rep_thm thm;

       val prems = Logic.strip_imp_prems prop;

       val concl = Drule.strip_imp_concl (cprop_of thm);

       val (lhs, rhs) = Drule.dest_equals concl handle TERM _ =>

         raise SIMPLIFIER ("Rewrite rule not a meta-equality", thm)

       val elhs = snd (Drule.dest_equals (cprop_of (Thm.eta_conversion lhs)));

       val elhs = if elhs=lhs then lhs else elhs (* try to share *)

       val erhs = Pattern.eta_contract (term_of rhs);

       val perm = var_perm (term_of elhs, erhs) andalso not (term_of elhs aconv erhs)

                  andalso not (is_Var (term_of elhs))

   in (sign, prems, term_of lhs, elhs, term_of rhs, perm) end;

 fun decomp_simp' thm =

   let val (_, _, lhs, _, rhs, _) = decomp_simp thm in

     if Thm.nprems_of thm > 0 then raise SIMPLIFIER ("Bad conditional rewrite rule", thm)

     else (lhs, rhs)

   end;

 fun mk_eq_True (Mss{mk_rews={mk_eq_True,...},...}) (thm, name) =

   case mk_eq_True thm of

     None => []

   | Some eq_True =>

       let val (_,_,lhs,elhs,_,_) = decomp_simp eq_True

       in [{thm=eq_True, name=name, lhs=lhs, elhs=elhs, perm=false}] end;

 (* create the rewrite rule and possibly also the ==True variant,

    in case there are extra vars on the rhs *)

 fun rrule_eq_True(thm,name,lhs,elhs,rhs,mss,thm2) =

   let val rrule = {thm=thm, name=name, lhs=lhs, elhs=elhs, perm=false}

   in if (term_varnames rhs)  subset (term_varnames lhs) andalso

         (term_tvars rhs) subset (term_tvars lhs)

      then [rrule]

      else mk_eq_True mss (thm2, name) @ [rrule]

   end;

 fun mk_rrule mss (thm, name) =

   let val (_,prems,lhs,elhs,rhs,perm) = decomp_simp thm

   in if perm then [{thm=thm, name=name, lhs=lhs, elhs=elhs, perm=true}] else

      (* weak test for loops: *)

      if rewrite_rule_extra_vars prems lhs rhs orelse

         is_Var (term_of elhs)

      then mk_eq_True mss (thm, name)

      else rrule_eq_True(thm,name,lhs,elhs,rhs,mss,thm)

   end;

 fun orient_rrule mss (thm, name) =

   let val (sign,prems,lhs,elhs,rhs,perm) = decomp_simp thm

   in if perm then [{thm=thm, name=name, lhs=lhs, elhs=elhs, perm=true}]

      else if reorient sign prems lhs rhs

           then if reorient sign prems rhs lhs

                then mk_eq_True mss (thm, name)

                else let val Mss{mk_rews={mk_sym,...},...} = mss

                     in case mk_sym thm of

                          None => []

                        | Some thm' =>

                            let val (_,_,lhs',elhs',rhs',_) = decomp_simp thm'

                            in rrule_eq_True(thm',name,lhs',elhs',rhs',mss,thm) end

                     end

           else rrule_eq_True(thm,name,lhs,elhs,rhs,mss,thm)

   end;

 fun extract_rews(Mss{mk_rews = {mk,...},...},thms) =

   flat (map (fn thm => map (rpair (Thm.name_of_thm thm)) (mk thm)) thms);

 fun orient_comb_simps comb mk_rrule (mss,thms) =

   let val rews = extract_rews(mss,thms)

       val rrules = flat (map mk_rrule rews)

   in foldl comb (mss,rrules) end

 (* Add rewrite rules explicitly; do not reorient! *)

 fun add_simps(mss,thms) =

   orient_comb_simps (insert_rrule false) (mk_rrule mss) (mss,thms);

 fun mss_of thms = foldl (insert_rrule false) (empty_mss, flat

   (map (fn thm => mk_rrule empty_mss (thm, Thm.name_of_thm thm)) thms));

 fun extract_safe_rrules(mss,thm) =

   flat (map (orient_rrule mss) (extract_rews(mss,[thm])));

 (* del_simps *)

 fun del_rrule(mss as Mss {rules,...},

               rrule as {thm, elhs, ...}) =

   (upd_rules(mss, Net.delete_term ((term_of elhs, rrule), rules, eq_rrule))

    handle Net.DELETE =>

      (prthm true "Rewrite rule not in simpset:" thm; mss));

 fun del_simps(mss,thms) =

   orient_comb_simps del_rrule (map mk_rrule2 o mk_rrule mss) (mss,thms);

 (* add_congs *)

 fun is_full_cong_prems [] varpairs = null varpairs

   | is_full_cong_prems (p::prems) varpairs =

     (case Logic.strip_assums_concl p of

        Const("==",_) $ lhs $ rhs =>

          let val (x,xs) = strip_comb lhs and (y,ys) = strip_comb rhs

          in is_Var x  andalso  forall is_Bound xs  andalso

             null(findrep(xs))  andalso xs=ys andalso

             (x,y) mem varpairs andalso

             is_full_cong_prems prems (varpairs\(x,y))

          end

      | _ => false);

 fun is_full_cong thm =

 let val prems = prems_of thm

     and concl = concl_of thm

     val (lhs,rhs) = Logic.dest_equals concl

     val (f,xs) = strip_comb lhs

     and (g,ys) = strip_comb rhs

 in

   f=g andalso null(findrep(xs@ys)) andalso length xs = length ys andalso

   is_full_cong_prems prems (xs ~~ ys)

 end

 fun cong_name (Const (a, _)) = Some a

   | cong_name (Free (a, _)) = Some ("Free: " ^ a)

   | cong_name _ = None;

 fun add_cong (Mss {rules,congs,procs,bounds,prems,mk_rews,termless,depth}, thm) =

   let

     val (lhs, _) = Drule.dest_equals (Drule.strip_imp_concl (cprop_of thm)) handle TERM _ =>

       raise SIMPLIFIER ("Congruence not a meta-equality", thm);

 (*   val lhs = Pattern.eta_contract lhs; *)

     val a = (case cong_name (head_of (term_of lhs)) of

         Some a => a

       | None =>

         raise SIMPLIFIER ("Congruence must start with a constant or free variable", thm));

     val (alist,weak) = congs

     val alist2 = overwrite_warn (alist, (a,{lhs=lhs, thm=thm}))

            ("Overwriting congruence rule for " ^ quote a);

     val weak2 = if is_full_cong thm then weak else a::weak

   in

     mk_mss (rules,(alist2,weak2),procs,bounds,prems,mk_rews,termless,depth)

   end;

 val (op add_congs) = foldl add_cong;

 (* del_congs *)

 fun del_cong (Mss {rules,congs,procs,bounds,prems,mk_rews,termless,depth}, thm) =

   let

     val (lhs, _) = Logic.dest_equals (concl_of thm) handle TERM _ =>

       raise SIMPLIFIER ("Congruence not a meta-equality", thm);

 (*   val lhs = Pattern.eta_contract lhs; *)

     val a = (case cong_name (head_of lhs) of

         Some a => a

       | None =>

         raise SIMPLIFIER ("Congruence must start with a constant", thm));

     val (alist,_) = congs

     val alist2 = filter (fn (x,_)=> x<>a) alist

     val weak2 = mapfilter (fn(a,{thm,...}) => if is_full_cong thm then None

                                               else Some a)

                    alist2

   in

     mk_mss (rules,(alist2,weak2),procs,bounds,prems,mk_rews,termless,depth)

   end;

 val (op del_congs) = foldl del_cong;

 (* add_simprocs *)

 fun add_proc (mss as Mss {rules,congs,procs,bounds,prems,mk_rews,termless,depth},

     (name, lhs, proc, id)) =

   let val {sign, t, ...} = rep_cterm lhs

   in (trace_term false ("Adding simplification procedure " ^ quote name ^ " for")

       sign t;

     mk_mss (rules, congs,

       Net.insert_term ((t, mk_simproc (name, proc, lhs, id)), procs, eq_simproc)

         handle Net.INSERT =>

             (warning ("Ignoring duplicate simplification procedure \""

                       ^ name ^ "\"");

              procs),

         bounds, prems, mk_rews, termless,depth))

   end;

 fun add_simproc (mss, (name, lhss, proc, id)) =

   foldl add_proc (mss, map (fn lhs => (name, lhs, proc, id)) lhss);

 val add_simprocs = foldl add_simproc;

 (* del_simprocs *)

 fun del_proc (mss as Mss {rules,congs,procs,bounds,prems,mk_rews,termless,depth},

     (name, lhs, proc, id)) =

   mk_mss (rules, congs,

     Net.delete_term ((term_of lhs, mk_simproc (name, proc, lhs, id)), procs, eq_simproc)

       handle Net.DELETE =>

           (warning ("Simplification procedure \"" ^ name ^

                        "\" not in simpset"); procs),

       bounds, prems, mk_rews, termless, depth);

 fun del_simproc (mss, (name, lhss, proc, id)) =

   foldl del_proc (mss, map (fn lhs => (name, lhs, proc, id)) lhss);

 val del_simprocs = foldl del_simproc;

 (* prems *)

 fun add_prems (Mss {rules,congs,procs,bounds,prems,mk_rews,termless,depth}, thms) =

   mk_mss (rules, congs, procs, bounds, thms @ prems, mk_rews, termless, depth);

 fun prems_of_mss (Mss {prems, ...}) = prems;

 (* mk_rews *)

 fun set_mk_rews

   (Mss {rules, congs, procs, bounds, prems, mk_rews, termless, depth}, mk) =

     mk_mss (rules, congs, procs, bounds, prems,

             {mk=mk, mk_sym= #mk_sym mk_rews, mk_eq_True= #mk_eq_True mk_rews},

             termless, depth);

 fun set_mk_sym

   (Mss {rules,congs,procs,bounds,prems,mk_rews,termless,depth}, mk_sym) =

     mk_mss (rules, congs, procs, bounds, prems,

             {mk= #mk mk_rews, mk_sym= mk_sym, mk_eq_True= #mk_eq_True mk_rews},

             termless,depth);

 fun set_mk_eq_True

   (Mss {rules,congs,procs,bounds,prems,mk_rews,termless,depth}, mk_eq_True) =

     mk_mss (rules, congs, procs, bounds, prems,

             {mk= #mk mk_rews, mk_sym= #mk_sym mk_rews, mk_eq_True= mk_eq_True},

             termless,depth);

 fun get_mk_rews    (Mss {mk_rews,...}) = #mk         mk_rews

 fun get_mk_sym     (Mss {mk_rews,...}) = #mk_sym     mk_rews

 fun get_mk_eq_True (Mss {mk_rews,...}) = #mk_eq_True mk_rews

 (* termless *)

 fun set_termless

   (Mss {rules, congs, procs, bounds, prems, mk_rews, depth, ...}, termless) =

     mk_mss (rules, congs, procs, bounds, prems, mk_rews, termless, depth);

 (** rewriting **)

 (*

   Uses conversions, see:

     L C Paulson, A higher-order implementation of rewriting,

     Science of Computer Programming 3 (1983), pages 119-149.

 *)

 val dest_eq = Drule.dest_equals o cprop_of;

 val lhs_of = fst o dest_eq;

 val rhs_of = snd o dest_eq;

 fun check_conv msg thm thm' =

   let

     val thm'' = transitive thm (transitive

       (symmetric (Drule.beta_eta_conversion (lhs_of thm'))) thm')

   in (if msg then trace_thm "SUCCEEDED" thm' else (); Some thm'') end

   handle THM _ =>

     let val {sign, prop = _ $ _ $ prop0, ...} = rep_thm thm;

     in

       (trace_thm "Proved wrong thm (Check subgoaler?)" thm';

        trace_term false "Should have proved:" sign prop0;

        None)

     end;

 (* mk_procrule *)

 fun mk_procrule thm =

   let val (_,prems,lhs,elhs,rhs,_) = decomp_simp thm

   in if rewrite_rule_extra_vars prems lhs rhs

      then (prthm true "Extra vars on rhs:" thm; [])

      else [mk_rrule2{thm=thm, name="", lhs=lhs, elhs=elhs, perm=false}]

   end;

 (* conversion to apply the meta simpset to a term *)

 (* Since the rewriting strategy is bottom-up, we avoid re-normalizing already

    normalized terms by carrying around the rhs of the rewrite rule just

    applied. This is called the `skeleton'. It is decomposed in parallel

    with the term. Once a Var is encountered, the corresponding term is

    already in normal form.

    skel0 is a dummy skeleton that is to enforce complete normalization.

 *)

 val skel0 = Bound 0;

 (* Use rhs as skeleton only if the lhs does not contain unnormalized bits.

    The latter may happen iff there are weak congruence rules for constants

    in the lhs.

 *)

 fun uncond_skel((_,weak),(lhs,rhs)) =

   if null weak then rhs (* optimization *)

   else if exists_Const (fn (c,_) => c mem weak) lhs then skel0

        else rhs;

 (* Behaves like unconditional rule if rhs does not contain vars not in the lhs.

    Otherwise those vars may become instantiated with unnormalized terms

    while the premises are solved.

 *)

 fun cond_skel(args as (congs,(lhs,rhs))) =

   if term_varnames rhs subset term_varnames lhs then uncond_skel(args)

   else skel0;

 (*

   we try in order:

     (1) beta reduction

     (2) unconditional rewrite rules

     (3) conditional rewrite rules

     (4) simplification procedures

   IMPORTANT: rewrite rules must not introduce new Vars or TVars!

 *)

 fun rewritec (prover, signt, maxt)

              (mss as Mss{rules, procs, termless, prems, congs, depth,...}) t =

   let

     val eta_thm = Thm.eta_conversion t;

     val eta_t' = rhs_of eta_thm;

     val eta_t = term_of eta_t';

     val tsigt = Sign.tsig_of signt;

     fun rew {thm, name, lhs, elhs, fo, perm} =

       let

         val {sign, prop, maxidx, ...} = rep_thm thm;

         val _ = if Sign.subsig (sign, signt) then ()

                 else (prthm true "Ignoring rewrite rule from different theory:" thm;

                       raise Pattern.MATCH);

         val (rthm, elhs') = if maxt = ~1 then (thm, elhs)

           else (Thm.incr_indexes (maxt+1) thm, Thm.cterm_incr_indexes (maxt+1) elhs);

         val insts = if fo then Thm.cterm_first_order_match (elhs', eta_t')

                           else Thm.cterm_match (elhs', eta_t');

         val thm' = Thm.instantiate insts (Thm.rename_boundvars lhs eta_t rthm);

         val prop' = Thm.prop_of thm';

         val unconditional = (Logic.count_prems (prop',0) = 0);

         val (lhs', rhs') = Logic.dest_equals (Logic.strip_imp_concl prop')

       in

         if perm andalso not (termless (rhs', lhs'))

         then (trace_named_thm "Cannot apply permutative rewrite rule" (thm, name);

               trace_thm "Term does not become smaller:" thm'; None)

         else (trace_named_thm "Applying instance of rewrite rule" (thm, name);

            if unconditional

            then

              (trace_thm "Rewriting:" thm';

               let val lr = Logic.dest_equals prop;

                   val Some thm'' = check_conv false eta_thm thm'

               in Some (thm'', uncond_skel (congs, lr)) end)

            else

              (trace_thm "Trying to rewrite:" thm';

               case incr_depth mss of

                 None => (trace_thm "FAILED - reached depth limit" thm'; None)

               | Some mss =>

               (case prover mss thm' of

                 None       => (trace_thm "FAILED" thm'; None)

               | Some thm2 =>

                   (case check_conv true eta_thm thm2 of

                      None => None |

                      Some thm2' =>

                        let val concl = Logic.strip_imp_concl prop

                            val lr = Logic.dest_equals concl

                        in Some (thm2', cond_skel (congs, lr)) end))))

       end

     fun rews [] = None

       | rews (rrule :: rrules) =

           let val opt = rew rrule handle Pattern.MATCH => None

           in case opt of None => rews rrules | some => some end;

     fun sort_rrules rrs = let

       fun is_simple({thm, ...}:rrule) = case Thm.prop_of thm of

                                       Const("==",_) $ _ $ _ => true

                                       | _                   => false

       fun sort []        (re1,re2) = re1 @ re2

         | sort (rr::rrs) (re1,re2) = if is_simple rr

                                      then sort rrs (rr::re1,re2)

                                      else sort rrs (re1,rr::re2)

     in sort rrs ([],[]) end

     fun proc_rews ([]:simproc list) = None

       | proc_rews ({name, proc, lhs, ...} :: ps) =

           if Pattern.matches tsigt (term_of lhs, term_of t) then

             (debug_term false ("Trying procedure " ^ quote name ^ " on:") signt eta_t;

              case transform_failure (curry SIMPROC_FAIL name)

                  (fn () => proc signt prems eta_t) () of

                None => (debug false "FAILED"; proc_rews ps)

              | Some raw_thm =>

                  (trace_thm ("Procedure " ^ quote name ^ " produced rewrite rule:") raw_thm;

                   (case rews (mk_procrule raw_thm) of

                     None => (trace_cterm true ("IGNORED result of simproc " ^ quote name ^

                       " -- does not match") t; proc_rews ps)

                   | some => some)))

           else proc_rews ps;

   in case eta_t of

        Abs _ $ _ => Some (transitive eta_thm

          (beta_conversion false eta_t'), skel0)

      | _ => (case rews (sort_rrules (Net.match_term rules eta_t)) of

                None => proc_rews (Net.match_term procs eta_t)

              | some => some)

   end;

 (* conversion to apply a congruence rule to a term *)

 fun congc (prover,signt,maxt) {thm=cong,lhs=lhs} t =

   let val sign = Thm.sign_of_thm cong

       val _ = if Sign.subsig (sign, signt) then ()

                  else error("Congruence rule from different theory")

       val rthm = if maxt = ~1 then cong else Thm.incr_indexes (maxt+1) cong;

       val rlhs = fst (Drule.dest_equals (Drule.strip_imp_concl (cprop_of rthm)));

       val insts = Thm.cterm_match (rlhs, t)

       (* Pattern.match can raise Pattern.MATCH;

          is handled when congc is called *)

       val thm' = Thm.instantiate insts (Thm.rename_boundvars (term_of rlhs) (term_of t) rthm);

       val unit = trace_thm "Applying congruence rule:" thm';

       fun err (msg, thm) = (trace_thm msg thm; None)

   in case prover thm' of

        None => err ("Congruence proof failed.  Could not prove", thm')

      | Some thm2 => (case check_conv true (Drule.beta_eta_conversion t) thm2 of

           None => err ("Congruence proof failed.  Should not have proved", thm2)

         | Some thm2' =>

             if op aconv (pairself term_of (dest_equals (cprop_of thm2')))

             then None else Some thm2')

   end;

 val (cA, (cB, cC)) =

   apsnd dest_equals (dest_implies (hd (cprems_of Drule.imp_cong)));

 fun transitive1 None None = None

   | transitive1 (Some thm1) None = Some thm1

   | transitive1 None (Some thm2) = Some thm2

   | transitive1 (Some thm1) (Some thm2) = Some (transitive thm1 thm2)

 fun transitive2 thm = transitive1 (Some thm);

 fun transitive3 thm = transitive1 thm o Some;

 fun bottomc ((simprem,useprem,mutsimp), prover, sign, maxidx) =

   let

     fun botc skel mss t =

           if is_Var skel then None

           else

           (case subc skel mss t of

              some as Some thm1 =>

                (case rewritec (prover, sign, maxidx) mss (rhs_of thm1) of

                   Some (thm2, skel2) =>

                     transitive2 (transitive thm1 thm2)

                       (botc skel2 mss (rhs_of thm2))

                 | None => some)

            | None =>

                (case rewritec (prover, sign, maxidx) mss t of

                   Some (thm2, skel2) => transitive2 thm2

                     (botc skel2 mss (rhs_of thm2))

                 | None => None))

     and try_botc mss t =

           (case botc skel0 mss t of

              Some trec1 => trec1 | None => (reflexive t))

     and subc skel

           (mss as Mss{rules,congs,procs,bounds,prems,mk_rews,termless,depth}) t0 =

        (case term_of t0 of

            Abs (a, T, t) =>

              let val b = variant bounds a

                  val (v, t') = Thm.dest_abs (Some ("." ^ b)) t0

                  val mss' = mk_mss (rules, congs, procs, b :: bounds, prems, mk_rews, termless,depth)

                  val skel' = case skel of Abs (_, _, sk) => sk | _ => skel0

              in case botc skel' mss' t' of

                   Some thm => Some (abstract_rule a v thm)

                 | None => None

              end

          | t $ _ => (case t of

              Const ("==>", _) $ _  => impc t0 mss

            | Abs _ =>

                let val thm = beta_conversion false t0

                in case subc skel0 mss (rhs_of thm) of

                     None => Some thm

                   | Some thm' => Some (transitive thm thm')

                end

            | _  =>

                let fun appc () =

                      let

                        val (tskel, uskel) = case skel of

                            tskel $ uskel => (tskel, uskel)

                          | _ => (skel0, skel0);

                        val (ct, cu) = Thm.dest_comb t0

                      in

                      (case botc tskel mss ct of

                         Some thm1 =>

                           (case botc uskel mss cu of

                              Some thm2 => Some (combination thm1 thm2)

                            | None => Some (combination thm1 (reflexive cu)))

                       | None =>

                           (case botc uskel mss cu of

                              Some thm1 => Some (combination (reflexive ct) thm1)

                            | None => None))

                      end

                    val (h, ts) = strip_comb t

                in case cong_name h of

                     Some a =>

                       (case assoc_string (fst congs, a) of

                          None => appc ()

                        | Some cong =>

 (* post processing: some partial applications h t1 ... tj, j <= length ts,

    may be a redex. Example: map (%x.x) = (%xs.xs) wrt map_cong *)

                           (let

                              val thm = congc (prover mss, sign, maxidx) cong t0;

                              val t = if_none (apsome rhs_of thm) t0;

                              val (cl, cr) = Thm.dest_comb t

                              val dVar = Var(("", 0), dummyT)

                              val skel =

                                list_comb (h, replicate (length ts) dVar)

                            in case botc skel mss cl of

                                 None => thm

                               | Some thm' => transitive3 thm

                                   (combination thm' (reflexive cr))

                            end handle TERM _ => error "congc result"

                                     | Pattern.MATCH => appc ()))

                   | _ => appc ()

                end)

          | _ => None)

     and impc ct mss =

       if mutsimp then mut_impc0 [] ct [] [] mss else nonmut_impc ct mss

     and rules_of_prem mss prem =

       if maxidx_of_term (term_of prem) <> ~1

       then (trace_cterm true

         "Cannot add premise as rewrite rule because it contains (type) unknowns:" prem; ([], None))

       else

         let val asm = assume prem

         in (extract_safe_rrules (mss, asm), Some asm) end

     and add_rrules (rrss, asms) mss =

       add_prems (foldl (insert_rrule true) (mss, flat rrss), mapfilter I asms)

     and disch r (prem, eq) =

       let

         val (lhs, rhs) = dest_eq eq;

         val eq' = implies_elim (Thm.instantiate

           ([], [(cA, prem), (cB, lhs), (cC, rhs)]) Drule.imp_cong)

           (implies_intr prem eq)

       in if not r then eq' else

         let

           val (prem', concl) = dest_implies lhs;

           val (prem'', _) = dest_implies rhs

         in transitive (transitive

           (Thm.instantiate ([], [(cA, prem'), (cB, prem), (cC, concl)])

              Drule.swap_prems_eq) eq')

           (Thm.instantiate ([], [(cA, prem), (cB, prem''), (cC, concl)])

              Drule.swap_prems_eq)

         end

       end

     and rebuild [] _ _ _ _ eq = eq

       | rebuild (prem :: prems) concl (rrs :: rrss) (asm :: asms) mss eq =

           let

             val mss' = add_rrules (rev rrss, rev asms) mss;

             val concl' =

               Drule.mk_implies (prem, if_none (apsome rhs_of eq) concl);

             val dprem = apsome (curry (disch false) prem)

           in case rewritec (prover, sign, maxidx) mss' concl' of

               None => rebuild prems concl' rrss asms mss (dprem eq)

             | Some (eq', _) => transitive2 (foldl (disch false o swap)

                   (the (transitive3 (dprem eq) eq'), prems))

                 (mut_impc0 (rev prems) (rhs_of eq') (rev rrss) (rev asms) mss)

           end

     and mut_impc0 prems concl rrss asms mss =

       let

         val prems' = strip_imp_prems concl;

         val (rrss', asms') = split_list (map (rules_of_prem mss) prems')

       in mut_impc (prems @ prems') (strip_imp_concl concl) (rrss @ rrss')

         (asms @ asms') [] [] [] [] mss ~1 ~1

       end

     and mut_impc [] concl [] [] prems' rrss' asms' eqns mss changed k =

         transitive1 (foldl (fn (eq2, (eq1, prem)) => transitive1 eq1

             (apsome (curry (disch false) prem) eq2)) (None, eqns ~~ prems'))

           (if changed > 0 then

              mut_impc (rev prems') concl (rev rrss') (rev asms')

                [] [] [] [] mss ~1 changed

            else rebuild prems' concl rrss' asms' mss

              (botc skel0 (add_rrules (rev rrss', rev asms') mss) concl))

       | mut_impc (prem :: prems) concl (rrs :: rrss) (asm :: asms)

           prems' rrss' asms' eqns mss changed k =

         case (if k = 0 then None else botc skel0 (add_rrules

           (rev rrss' @ rrss, rev asms' @ asms) mss) prem) of

             None => mut_impc prems concl rrss asms (prem :: prems')

               (rrs :: rrss') (asm :: asms') (None :: eqns) mss changed

               (if k = 0 then 0 else k - 1)

           | Some eqn =>

             let

               val prem' = rhs_of eqn;

               val tprems = map term_of prems;

               val i = 1 + foldl Int.max (~1, map (fn p =>

                 find_index_eq p tprems) (#hyps (rep_thm eqn)));

               val (rrs', asm') = rules_of_prem mss prem'

             in mut_impc prems concl rrss asms (prem' :: prems')

               (rrs' :: rrss') (asm' :: asms') (Some (foldr (disch true)

                 (take (i, prems), Drule.imp_cong' eqn (reflexive (Drule.list_implies

                   (drop (i, prems), concl))))) :: eqns) mss (length prems') ~1

             end

      (* legacy code - only for backwards compatibility *)

      and nonmut_impc ct mss =

        let val (prem, conc) = dest_implies ct;

            val thm1 = if simprem then botc skel0 mss prem else None;

            val prem1 = if_none (apsome rhs_of thm1) prem;

            val mss1 = if not useprem then mss else add_rrules

              (apsnd single (apfst single (rules_of_prem mss prem1))) mss

        in (case botc skel0 mss1 conc of

            None => (case thm1 of

                None => None

              | Some thm1' => Some (Drule.imp_cong' thm1' (reflexive conc)))

          | Some thm2 =>

            let val thm2' = disch false (prem1, thm2)

            in (case thm1 of

                None => Some thm2'

              | Some thm1' =>

                  Some (transitive (Drule.imp_cong' thm1' (reflexive conc)) thm2'))

            end)

        end

  in try_botc end;

 (*** Meta-rewriting: rewrites t to u and returns the theorem t==u ***)

 (*

   Parameters:

     mode = (simplify A,

             use A in simplifying B,

             use prems of B (if B is again a meta-impl.) to simplify A)

            when simplifying A ==> B

     mss: contains equality theorems of the form [|p1,...|] ==> t==u

     prover: how to solve premises in conditional rewrites and congruences

 *)

 fun rewrite_cterm mode prover mss ct =

   let val {sign, t, maxidx, ...} = rep_cterm ct

       val Mss{depth, ...} = mss

   in trace_cterm false "SIMPLIFIER INVOKED ON THE FOLLOWING TERM:" ct;

      simp_depth := depth;

      bottomc (mode, prover, sign, maxidx) mss ct

   end

   handle THM (s, _, thms) =>

     error ("Exception THM was raised in simplifier:\n" ^ s ^ "\n" ^

       Pretty.string_of (Display.pretty_thms thms));

 (*Rewrite a cterm*)

 fun rewrite_aux _ _ [] = (fn ct => Thm.reflexive ct)

   | rewrite_aux prover full thms = rewrite_cterm (full, false, false) prover (mss_of thms);

 (*Rewrite a theorem*)

 fun simplify_aux _ _ [] = (fn th => th)

   | simplify_aux prover full thms =

       Drule.fconv_rule (rewrite_cterm (full, false, false) prover (mss_of thms));

 fun rewrite_thm mode prover mss = Drule.fconv_rule (rewrite_cterm mode prover mss);

 (*Rewrite the subgoals of a proof state (represented by a theorem) *)

 fun rewrite_goals_rule_aux _ []   th = th

   | rewrite_goals_rule_aux prover thms th =

       Drule.fconv_rule (Drule.goals_conv (K true) (rewrite_cterm (true, true, false) prover

         (mss_of thms))) th;

 (*Rewrite the subgoal of a proof state (represented by a theorem) *)

 fun rewrite_goal_rule mode prover mss i thm =

   if 0 < i  andalso  i <= nprems_of thm

   then Drule.fconv_rule (Drule.goals_conv (fn j => j=i) (rewrite_cterm mode prover mss)) thm

   else raise THM("rewrite_goal_rule",i,[thm]);

 (*simple term rewriting -- without proofs*)

 fun rewrite_term sg rules procs =

   Pattern.rewrite_term (Sign.tsig_of sg) (map decomp_simp' rules) procs;

 end;

 structure BasicMetaSimplifier: BASIC_META_SIMPLIFIER = MetaSimplifier;

 open BasicMetaSimplifier;