src/HOL/Tools/record_package.ML

reimplementation of HOL records; only one type is created for
each record extension, instead of one type for each field. See NEWS.

(*  Title:      HOL/Tools/record_package.ML
    ID:         $Id$
    Author:     Wolfgang Naraschewski, Norbert Schirmer and Markus Wenzel, TU Muenchen
    License:    GPL (GNU GENERAL PUBLIC LICENSE)

Extensible records with structural subtyping in HOL.
*)

signature BASIC_RECORD_PACKAGE =
sig
  val record_simproc: simproc
  val record_eq_simproc: simproc
  val record_upd_simproc: simproc
  val record_split_simproc: (term -> bool) -> simproc
  val record_ex_sel_eq_simproc: simproc
  val record_split_tac: int -> tactic
  val record_split_simp_tac: (term -> bool) -> int -> tactic
  val record_split_name: string
  val record_split_wrapper: string * wrapper
  val print_record_type_abbr: bool ref
  val print_record_type_as_fields: bool ref 
end;

signature RECORD_PACKAGE =
sig
  include BASIC_RECORD_PACKAGE
  val quiet_mode: bool ref
  val updateN: string
  val ext_typeN: string
  val last_extT: typ -> (string * typ list) option
  val dest_recTs : typ -> (string * typ list) list
  val get_extension: Sign.sg -> Symtab.key -> (string * typ list) option
  val print_records: theory -> unit
  val add_record: string list * string -> string option -> (string * string * mixfix) list 
                  -> theory -> theory
  val add_record_i: string list * string -> (typ list * string) option 
                    -> (string * typ * mixfix) list -> theory -> theory
  val setup: (theory -> theory) list
end;


structure RecordPackage :RECORD_PACKAGE =    
struct

val rec_UNIV_I = thm "rec_UNIV_I";
val rec_True_simp = thm "rec_True_simp";
val Pair_eq = thm "Product_Type.Pair_eq";
val atomize_all = thm "HOL.atomize_all";
val atomize_imp = thm "HOL.atomize_imp";
val triv_goal   = thm "triv_goal";
val prop_subst  = thm "prop_subst";
val Pair_sel_convs = [fst_conv,snd_conv];



(** name components **)

val rN = "r";
val moreN = "more";
val schemeN = "_scheme";
val ext_typeN = "_ext_type"; 
val extN ="_ext";
val ext_dest = "_val";
val updateN = "_update";
val schemeN = "_scheme";
val makeN = "make";
val fields_selN = "fields";
val extendN = "extend";
val truncateN = "truncate";

(*see typedef_package.ML*)
val RepN = "Rep_";
val AbsN = "Abs_";

(*** utilities ***)


fun last [] = error "RecordPackage.last: empty list"
  | last [x] = x
  | last (x::xs) = last xs;

fun but_last [] = error "RecordPackage.but_last: empty list"
  | but_last [x] = []
  | but_last (x::xs) = x::but_last xs;

fun remdups [] = []
  | remdups (x::xs) = x::remdups (filter_out (fn y => y=x) xs);

fun is_suffix sfx s = is_some (try (unsuffix sfx) s);

(* messages *)

val quiet_mode = ref false;
fun message s = if ! quiet_mode then () else writeln s;

(* syntax *)

fun prune n xs = Library.drop (n, xs);
fun prefix_base s = NameSpace.map_base (fn bname => s ^ bname);

val Trueprop = HOLogic.mk_Trueprop;
fun All xs t = Term.list_all_free (xs, t);

infix 9 $$;
infix 0 :== ===;
infixr 0 ==>;

val (op $$) = Term.list_comb;
val (op :==) = Logic.mk_defpair;
val (op ===) = Trueprop o HOLogic.mk_eq;
val (op ==>) = Logic.mk_implies;

(* morphisms *)

fun mk_RepN name = suffix ext_typeN (prefix_base RepN name);
fun mk_AbsN name = suffix ext_typeN (prefix_base AbsN name);

fun mk_Rep name repT absT  =
  Const (suffix ext_typeN (prefix_base RepN name),absT --> repT);

fun mk_Abs name repT absT =
  Const (mk_AbsN name,repT --> absT);

(* constructor *)

fun mk_extC (name,T) Ts  = (suffix extN name, Ts ---> T);

fun mk_ext (name,T) ts =
  let val Ts = map fastype_of ts
  in list_comb (Const (mk_extC (name,T) Ts),ts) end;

(* selector *)

fun mk_selC sT (c,T) = (c,sT --> T);

fun mk_sel s (c,T) =
  let val sT = fastype_of s
  in Const (mk_selC sT (c,T)) $ s end;

(* updates *)

fun mk_updC sT (c,T) = (suffix updateN c, T --> sT --> sT);

fun mk_upd c v s =
  let val sT = fastype_of s;
      val vT = fastype_of v;
  in Const (mk_updC sT (c, vT)) $ v $ s end;

(* types *)

fun dest_recT (typ as Type (c_ext_type, Ts as (T::_))) =
      (case try (unsuffix ext_typeN) c_ext_type of
        None => raise TYPE ("RecordPackage.dest_recT", [typ], [])
      | Some c => ((c, Ts), last Ts))
  | dest_recT typ = raise TYPE ("RecordPackage.dest_recT", [typ], []);

fun is_recT T =
  (case try dest_recT T of None => false | Some _ => true); 

fun dest_recTs T =
  let val ((c, Ts), U) = dest_recT T
  in (c, Ts) :: dest_recTs U
  end handle TYPE _ => [];

fun last_extT T =
  let val ((c, Ts), U) = dest_recT T
  in (case last_extT U of
        None => Some (c,Ts)
      | Some l => Some l)
  end handle TYPE _ => None

fun rec_id T = foldl (fn (s,(c,T)) => s ^ c) ("",dest_recTs T);

(*** extend theory by record definition ***)

(** record info **)

(* type record_info and parent_info  *)

type record_info =
 {args: (string * sort) list,
  parent: (typ list * string) option,
  fields: (string * typ) list,
  extension: (string * typ list),
  induct: thm
 };

fun make_record_info args parent fields extension induct =
 {args = args, parent = parent, fields = fields, extension = extension, 
  induct = induct}: record_info;


type parent_info =
 {name: string,
  fields: (string * typ) list,
  extension: (string * typ list),
  induct: thm
};

fun make_parent_info name fields extension induct =
 {name = name, fields = fields, extension = extension, induct = induct}: parent_info;

(* data kind 'HOL/record' *)

type record_data =
 {records: record_info Symtab.table,
  sel_upd:
   {selectors: unit Symtab.table,
    updates: string Symtab.table,
    simpset: Simplifier.simpset},
  equalities: thm Symtab.table,
  splits: (thm*thm*thm*thm) Symtab.table,    (* !!,!,EX - split-equalities,induct rule *) 
  extfields: (string*typ) list Symtab.table, (* maps extension to its fields *)
  fieldext: (string*typ list) Symtab.table   (* maps field to its extension *)
};

fun make_record_data records sel_upd equalities splits extfields fieldext =
 {records = records, sel_upd = sel_upd, 
  equalities = equalities, splits = splits, 
  extfields = extfields, fieldext = fieldext }: record_data;

structure RecordsArgs =
struct
  val name = "HOL/records";    
  type T = record_data;

  val empty =
    make_record_data Symtab.empty
      {selectors = Symtab.empty, updates = Symtab.empty, simpset = HOL_basic_ss}
      Symtab.empty Symtab.empty Symtab.empty Symtab.empty;

  val copy = I;
  val prep_ext = I;
  fun merge
   ({records = recs1,
     sel_upd = {selectors = sels1, updates = upds1, simpset = ss1},
     equalities = equalities1,
     splits = splits1,
     extfields = extfields1,
     fieldext = fieldext1},
    {records = recs2,
     sel_upd = {selectors = sels2, updates = upds2, simpset = ss2},
     equalities = equalities2, 
     splits = splits2,
     extfields = extfields2,
     fieldext = fieldext2}) =
    make_record_data  
      (Symtab.merge (K true) (recs1, recs2))
      {selectors = Symtab.merge (K true) (sels1, sels2),
        updates = Symtab.merge (K true) (upds1, upds2),
        simpset = Simplifier.merge_ss (ss1, ss2)}
      (Symtab.merge Thm.eq_thm (equalities1, equalities2))
      (Symtab.merge (fn ((a,b,c,d),(w,x,y,z)) 
                     => Thm.eq_thm (a,w) andalso Thm.eq_thm (b,x) andalso 
                        Thm.eq_thm (c,y) andalso Thm.eq_thm (d,z)) 
                    (splits1, splits2))
      (Symtab.merge (K true) (extfields1,extfields2))
      (Symtab.merge (K true) (fieldext1,fieldext2));

  fun print sg ({records = recs, ...}: record_data) =
    let
      val prt_typ = Sign.pretty_typ sg;

      fun pretty_parent None = []
        | pretty_parent (Some (Ts, name)) =
            [Pretty.block [prt_typ (Type (name, Ts)), Pretty.str " +"]];

      fun pretty_field (c, T) = Pretty.block
        [Pretty.str (Sign.cond_extern sg Sign.constK c), Pretty.str " ::",
          Pretty.brk 1, Pretty.quote (prt_typ T)];

      fun pretty_record (name, {args, parent, fields, ...}: record_info) =
        Pretty.block (Pretty.fbreaks (Pretty.block
          [prt_typ (Type (name, map TFree args)), Pretty.str " = "] ::
          pretty_parent parent @ map pretty_field fields));
    in map pretty_record (Symtab.dest recs) |> Pretty.chunks |> Pretty.writeln end;
end;

structure RecordsData = TheoryDataFun(RecordsArgs);
val print_records = RecordsData.print;

(* access 'records' *)

fun get_record thy name = Symtab.lookup (#records (RecordsData.get thy), name);

fun put_record name info thy =
  let
    val {records, sel_upd, equalities, splits,extfields,fieldext} = RecordsData.get thy;
    val data = make_record_data (Symtab.update ((name, info), records))
      sel_upd equalities splits extfields fieldext;
  in RecordsData.put data thy end;

(* access 'sel_upd' *)

fun get_sel_upd sg = #sel_upd (RecordsData.get_sg sg);

fun get_selectors sg name = Symtab.lookup (#selectors (get_sel_upd sg), name);
fun is_selector sg name = 
  case get_selectors sg (Sign.intern_const sg name) of 
     None => false
   | Some _ => true

                             
fun get_updates sg name = Symtab.lookup (#updates (get_sel_upd sg), name);
fun get_simpset sg = #simpset (get_sel_upd sg);

fun put_sel_upd names simps thy =
  let
    val sels = map (rpair ()) names;
    val upds = map (suffix updateN) names ~~ names;

    val {records, sel_upd = {selectors, updates, simpset}, 
      equalities, splits, extfields,fieldext} = RecordsData.get thy;
    val data = make_record_data records
      {selectors = Symtab.extend (selectors, sels),
        updates = Symtab.extend (updates, upds),
        simpset = Simplifier.addsimps (simpset, simps)}
       equalities splits extfields fieldext;
  in RecordsData.put data thy end;

(* access 'equalities' *)

fun add_record_equalities name thm thy =
  let
    val {records, sel_upd, equalities, splits, extfields,fieldext} = RecordsData.get thy;
    val data = make_record_data records sel_upd 
      (Symtab.update_new ((name, thm), equalities)) splits extfields fieldext;
  in RecordsData.put data thy end;

fun get_equalities sg name =
  Symtab.lookup (#equalities (RecordsData.get_sg sg), name);

(* access 'splits' *)

fun add_record_splits name thmP thy =
  let
    val {records, sel_upd, equalities, splits, extfields,fieldext} = RecordsData.get thy;
    val data = make_record_data records sel_upd 
      equalities (Symtab.update_new ((name, thmP), splits)) extfields fieldext;
  in RecordsData.put data thy end;

fun get_splits sg name =
  Symtab.lookup (#splits (RecordsData.get_sg sg), name);

(* extension of a record name *)
fun get_extension sg name =
 case Symtab.lookup (#records (RecordsData.get_sg sg),name) of
        Some s => Some (#extension s)
      | None => None;

(* access 'extfields' *)

fun add_extfields name fields thy =
  let
    val {records, sel_upd, equalities, splits, extfields, fieldext} = RecordsData.get thy;
    val data = make_record_data records sel_upd 
         equalities splits (Symtab.update_new ((name, fields), extfields)) fieldext;
  in RecordsData.put data thy end;

fun get_extfields sg name =
  Symtab.lookup (#extfields (RecordsData.get_sg sg), name);

(* access 'fieldext' *)

fun add_fieldext extname_types fields thy =
  let
    val {records, sel_upd, equalities, splits, extfields, fieldext} = RecordsData.get thy;
    val fieldext' = foldl (fn (table,field) => Symtab.update_new ((field,extname_types),table))  
                          (fieldext,fields);
    val data = make_record_data records sel_upd equalities splits extfields fieldext';
  in RecordsData.put data thy end;


fun get_fieldext sg name =
  Symtab.lookup (#fieldext (RecordsData.get_sg sg), name);

(* parent records *)

fun add_parents thy None parents = parents
  | add_parents thy (Some (types, name)) parents =
      let
        val sign = Theory.sign_of thy;
        fun err msg = error (msg ^ " parent record " ^ quote name);

        val {args, parent, fields, extension, induct} =
          (case get_record thy name of Some info => info | None => err "Unknown");
        val _ = if length types <> length args then err "Bad number of arguments for" else ();

        fun bad_inst ((x, S), T) =
          if Sign.of_sort sign (T, S) then None else Some x
        val bads = mapfilter bad_inst (args ~~ types);

        val inst = map fst args ~~ types;
        val subst = Term.map_type_tfree (fn (x, _) => the (assoc (inst, x)));
        val parent' = apsome (apfst (map subst)) parent;
        val fields' = map (apsnd subst) fields;
        val extension' = apsnd (map subst) extension;
      in
        conditional (not (null bads)) (fn () =>
          err ("Ill-sorted instantiation of " ^ commas bads ^ " in"));
        add_parents thy parent'
          (make_parent_info name fields' extension' induct::parents)
      end;


(** concrete syntax for records **)

(* parse translations *)

fun gen_field_tr mark sfx (t as Const (c, _) $ Const (name, _) $ arg) =
      if c = mark then Syntax.const (suffix sfx name) $ arg
      else raise TERM ("gen_field_tr: " ^ mark, [t])
  | gen_field_tr mark _ t = raise TERM ("gen_field_tr: " ^ mark, [t]);

fun gen_fields_tr sep mark sfx (tm as Const (c, _) $ t $ u) =
      if c = sep then gen_field_tr mark sfx t :: gen_fields_tr sep mark sfx u
      else [gen_field_tr mark sfx tm]
  | gen_fields_tr _ mark sfx tm = [gen_field_tr mark sfx tm];


fun record_update_tr [t, u] =
      foldr (op $) (rev (gen_fields_tr "_updates" "_update" updateN u), t)
  | record_update_tr ts = raise TERM ("record_update_tr", ts);

fun update_name_tr (Free (x, T) :: ts) = Free (suffix updateN x, T) $$ ts
  | update_name_tr (Const (x, T) :: ts) = Const (suffix updateN x, T) $$ ts
  | update_name_tr (((c as Const ("_constrain", _)) $ t $ ty) :: ts) =
      (c $ update_name_tr [t] $ (Syntax.const "fun" $ ty $ Syntax.const "dummy")) $$ ts
  | update_name_tr ts = raise TERM ("update_name_tr", ts);

fun dest_ext_field mark (t as (Const (c,_) $ Const (name,_) $ arg)) =
     if c = mark then (name,arg) else raise TERM ("dest_ext_field: " ^ mark, [t])
  | dest_ext_field _ t = raise TERM ("dest_ext_field", [t])

fun dest_ext_fields sep mark (trm as (Const (c,_) $ t $ u)) =
     if c = sep then dest_ext_field mark t::dest_ext_fields sep mark u
     else [dest_ext_field mark trm]
  | dest_ext_fields _ mark t = [dest_ext_field mark t]

fun gen_ext_fields_tr sep mark sfx more sg t =
  let 
    val fieldargs = dest_ext_fields sep mark t; 
    fun splitargs (field::fields) ((name,arg)::fargs) =
          if is_suffix name field
          then let val (args,rest) = splitargs fields fargs
               in (arg::args,rest) end
          else raise TERM ("gen_ext_fields_tr: expecting field " ^ field ^ 
                           " but got " ^ name, [t])
      | splitargs [] (fargs as (_::_)) = ([],fargs)
      | splitargs (_::_) [] = raise TERM ("gen_ext_fields_tr: expecting more fields", [t])
      | splitargs _ _ = ([],[]);

    fun mk_ext (fargs as (name,arg)::_) =
         (case get_fieldext sg (Sign.intern_const sg name) of
            Some (ext,_) => (case get_extfields sg ext of
                               Some flds 
                                 => let val (args,rest) = 
                                               splitargs (map fst (but_last flds)) fargs;
                                        val more' = mk_ext rest;  
                                    in list_comb (Syntax.const (suffix sfx ext),args@[more'])
                                    end
                             | None => raise TERM("gen_ext_fields_tr: no fields defined for "
                                                   ^ ext,[t]))
          | None => raise TERM ("gen_ext_fields_tr: "^ name ^" is no proper field",[t]))
      | mk_ext [] = more

  in mk_ext fieldargs end;   

fun gen_ext_type_tr sep mark sfx more sg t =
  let 
    val fieldargs = dest_ext_fields sep mark t; 
    fun splitargs (field::fields) ((name,arg)::fargs) =
          if is_suffix name field
          then let val (args,rest) = splitargs fields fargs
               in (arg::args,rest) end
          else raise TERM ("gen_ext_type_tr: expecting field " ^ field ^ 
                           " but got " ^ name, [t])
      | splitargs [] (fargs as (_::_)) = ([],fargs)
      | splitargs (_::_) [] = raise TERM ("gen_ext_type_tr: expecting more fields", [t])
      | splitargs _ _ = ([],[]);

    fun get_sort xs n = (case assoc (xs,n) of 
                                Some s => s 
                              | None => Sign.defaultS sg);
    fun to_type t = Sign.intern_typ sg 
                      (Syntax.typ_of_term (get_sort (Syntax.raw_term_sorts t)) I t);
 
    val tsig = Sign.tsig_of sg;
    fun unify (t,env) = Type.unify tsig env t; 
    
    fun mk_ext (fargs as (name,arg)::_) =
         (case get_fieldext sg (Sign.intern_const sg name) of
            Some (ext,alphas) => 
              (case get_extfields sg ext of
                 Some flds 
                  => (let
                       val flds' = but_last flds;
                       val types = map snd flds'; 
                       val (args,rest) = splitargs (map fst flds') fargs;
                       val vartypes = map Type.varifyT types;
                       val argtypes = map to_type args;
                       val (subst,_) = foldr unify (vartypes ~~ argtypes,(Vartab.empty,0));
                       val alphas' = map ((Syntax.term_of_typ (! Syntax.show_sorts)) o 
                                          (Envir.norm_type subst) o Type.varifyT) 
                                         (but_last alphas);
 
                       val more' = mk_ext rest;   
                     in list_comb (Syntax.const (suffix sfx ext),alphas'@[more']) 
                     end handle TUNIFY => raise 
                           TERM ("gen_ext_type_tr: type is no proper record (extension)", [t]))
               | None => raise TERM ("gen_ext_fields_tr: no fields defined for " ^ ext,[t]))
          | None => raise TERM ("gen_ext_fields_tr: "^ name ^" is no proper field",[t]))
      | mk_ext [] = more

  in mk_ext fieldargs end;   

fun gen_adv_record_tr sep mark sfx unit sg [t] = 
      gen_ext_fields_tr sep mark sfx unit sg t
  | gen_adv_record_tr _ _ _ _ _ ts = raise TERM ("gen_record_tr", ts);

fun gen_adv_record_scheme_tr sep mark sfx sg [t, more] = 
      gen_ext_fields_tr sep mark sfx more sg t 
  | gen_adv_record_scheme_tr _ _ _ _ ts = raise TERM ("gen_record_scheme_tr", ts);

fun gen_adv_record_type_tr sep mark sfx unit sg [t] = 
      gen_ext_type_tr sep mark sfx unit sg t
  | gen_adv_record_type_tr _ _ _ _ _ ts = raise TERM ("gen_record_tr", ts);

fun gen_adv_record_type_scheme_tr sep mark sfx sg [t, more] = 
      gen_ext_type_tr sep mark sfx more sg t 
  | gen_adv_record_type_scheme_tr _ _ _ _ ts = raise TERM ("gen_record_scheme_tr", ts);

val adv_record_tr = gen_adv_record_tr "_fields" "_field" extN HOLogic.unit;
val adv_record_scheme_tr = gen_adv_record_scheme_tr "_fields" "_field" extN;

val adv_record_type_tr = 
      gen_adv_record_type_tr "_field_types" "_field_type" ext_typeN 
        (Syntax.term_of_typ false (HOLogic.unitT));
val adv_record_type_scheme_tr = 
      gen_adv_record_type_scheme_tr "_field_types" "_field_type" ext_typeN;

val parse_translation =
 [("_record_update", record_update_tr),
  ("_update_name", update_name_tr)];

val adv_parse_translation = 
 [("_record",adv_record_tr),
  ("_record_scheme",adv_record_scheme_tr),
  ("_record_type",adv_record_type_tr),
  ("_record_type_scheme",adv_record_type_scheme_tr)];


(* print translations *)

val print_record_type_abbr = ref true;
val print_record_type_as_fields = ref true;

fun gen_field_upds_tr' mark sfx (tm as Const (name_field, _) $ t $ u) =
    (case try (unsuffix sfx) name_field of
      Some name =>
        apfst (cons (Syntax.const mark $ Syntax.free name $ t)) (gen_field_upds_tr' mark sfx u)
     | None => ([], tm))
  | gen_field_upds_tr' _ _ tm = ([], tm);

fun record_update_tr' tm =
  let val (ts, u) = gen_field_upds_tr' "_update" updateN tm in
    Syntax.const "_record_update" $ u $
      foldr1 (fn (v, w) => Syntax.const "_updates" $ v $ w) (rev ts)
  end;

fun gen_field_tr' sfx tr' name =
  let val name_sfx = suffix sfx name
  in (name_sfx, fn [t, u] => tr' (Syntax.const name_sfx $ t $ u) | _ => raise Match) end;

fun record_tr' sep mark record record_scheme unit sg t =
  let 
    fun field_lst t =
      (case strip_comb t of
        (Const (ext,_),args) 
         => (case try (unsuffix extN) (Sign.intern_const sg ext) of
               Some ext' 
               => (case get_extfields sg ext' of
                     Some flds 
                     => (let
                          val (f::fs) = but_last (map fst flds);
                          val flds' = Sign.extern sg Sign.constK f::map NameSpace.base fs; 
                          val (args',more) = split_last args; 
                         in (flds'~~args')@field_lst more end
                         handle LIST _ => [("",t)]) 
                   | None => [("",t)])
             | None => [("",t)])
       | _ => [("",t)])

    val (flds,(_,more)) = split_last (field_lst t);
    val flds' = map (fn (n,t)=>Syntax.const mark$Syntax.const n$t) flds;
    val flds'' = foldr1 (fn (x,y) => Syntax.const sep$x$y) flds';

  in if null flds then raise Match
     else if unit more  
          then Syntax.const record$flds'' 
          else Syntax.const record_scheme$flds''$more
  end

fun gen_record_tr' name = 
  let val name_sfx = suffix extN name;
      val unit = (fn Const ("Unity",_) => true | _ => false);
      fun tr' sg ts = record_tr' "_fields" "_field" "_record" "_record_scheme" unit sg 
                       (list_comb (Syntax.const name_sfx,ts))
  in (name_sfx,tr')
  end

fun print_translation names =
  map (gen_field_tr' updateN record_update_tr') names;

(* record_type_abbr_tr' tries to reconstruct the record name type abbreviation from *)
(* the (nested) extension types.                                                    *)
fun record_type_abbr_tr' default_tr' abbr alphas zeta lastExt schemeT sg tm =
  let
      (* tm is term representation of a (nested) field type. We first reconstruct the      *)
      (* type from tm so that we can continue on the type level rather then the term level.*)

      fun get_sort xs n = (case assoc (xs,n) of 
                             Some s => s 
                           | None => Sign.defaultS sg);

      val T = Sign.intern_typ sg (Syntax.typ_of_term (get_sort (Syntax.raw_term_sorts tm)) I tm) 
      val tsig = Sign.tsig_of sg

      fun mk_type_abbr subst name alphas = 
          let val abbrT = Type (name, map (fn a => TVar ((a,0),logicS)) alphas);
          in Syntax.term_of_typ (! Syntax.show_sorts) (Envir.norm_type subst abbrT) end;    

      fun unify rT T = fst (Type.unify tsig (Vartab.empty,0) (Type.varifyT rT,T))

   in if !print_record_type_abbr
      then (case last_extT T of
             Some (name,_) 
              => if name = lastExt 
                 then
		  (let val subst = unify schemeT T 
                   in 
                    if HOLogic.is_unitT (Envir.norm_type subst (TVar((zeta,0),Sign.defaultS sg)))
                    then mk_type_abbr subst abbr alphas
                    else mk_type_abbr subst (suffix schemeN abbr) (alphas@[zeta])
		   end handle TUNIFY => default_tr' sg tm)
                 else raise Match (* give print translation of specialised record a chance *)
            | _ => raise Match)
       else default_tr' sg tm
  end

fun record_type_tr' sep mark record record_scheme sg t =
  let
    fun get_sort xs n = (case assoc (xs,n) of 
                             Some s => s 
                           | None => Sign.defaultS sg);

    val T = Sign.intern_typ sg (Syntax.typ_of_term (get_sort (Syntax.raw_term_sorts t)) I t)

    val tsig = Sign.tsig_of sg
    fun unify (t,v) = Type.unify tsig v t;

    fun term_of_type T = Syntax.term_of_typ (!Syntax.show_sorts) (Sign.extern_typ sg T);
 
    fun field_lst T =
      (case T of
        Type (ext,args) 
         => (case try (unsuffix ext_typeN) ext of
               Some ext' 
               => (case get_extfields sg ext' of
                     Some flds 
                     => (case get_fieldext sg (fst (hd flds)) of
                           Some (_,alphas) 
                           => (let
                                val (f::fs) = but_last flds;
                                val flds' = apfst (Sign.extern sg Sign.constK) f
                                            ::map (apfst NameSpace.base) fs; 
                                val (args',more) = split_last args; 
                                val alphavars = map Type.varifyT (but_last alphas); 
                                val (subst,_)= foldr unify (alphavars~~args',(Vartab.empty,0));
                                val flds'' =map (apsnd ((Envir.norm_type subst)o(Type.varifyT)))
                                                flds';
                              in flds''@field_lst more end
                              handle TUNIFY => [("",T)] 
                                   | LIST _=> [("",T)])
                         | None => [("",T)])
                   | None => [("",T)])
             | None => [("",T)]) 
        | _ => [("",T)])

    val (flds,(_,moreT)) = split_last (field_lst T);
    val flds' = map (fn (n,T)=>Syntax.const mark$Syntax.const n$term_of_type T) flds;
    val flds'' = foldr1 (fn (x,y) => Syntax.const sep$x$y) flds';

  in if not (!print_record_type_as_fields) orelse null flds then raise Match
     else if moreT = HOLogic.unitT 
          then Syntax.const record$flds'' 
          else Syntax.const record_scheme$flds''$term_of_type moreT
  end
    

fun gen_record_type_tr' name = 
  let val name_sfx = suffix ext_typeN name;
      fun tr' sg ts = record_type_tr' "_field_types" "_field_type" 
                       "_record_type" "_record_type_scheme" sg 
                       (list_comb (Syntax.const name_sfx,ts))
  in (name_sfx,tr')
  end

     
fun gen_record_type_abbr_tr' abbr alphas zeta lastExt schemeT name =
  let val name_sfx = suffix ext_typeN name;
      val default_tr' = record_type_tr' "_field_types" "_field_type" 
                               "_record_type" "_record_type_scheme" 
      fun tr' sg ts = record_type_abbr_tr' default_tr' abbr alphas zeta lastExt schemeT sg
                         (list_comb (Syntax.const name_sfx,ts))
  in (name_sfx, tr') end;


(** record simprocs **)
fun quick_and_dirty_prove sg xs asms prop tac =
Tactic.prove sg xs asms prop
    (if !quick_and_dirty then (K (SkipProof.cheat_tac HOL.thy)) else tac);


fun prove_split_simp sg T prop =
  (case get_splits sg (rec_id T) of
     Some (all_thm,_,_,_) 
     => let val {sel_upd={simpset,...},...} = RecordsData.get_sg sg;
        in (quick_and_dirty_prove sg [] [] prop 
           (K (simp_tac (simpset addsimps [all_thm]) 1)))
        end
   | _ => error "RecordPackage.prove_split_simp:code should never been reached")

(* record_simproc *)
(* Simplifies selections of an record update:
 *  (1)  S (r(|S:=k|)) = k respectively
 *  (2)  S (r(|X:=k|)) = S r
 * The simproc skips multiple updates at once, eg:
 *  S (r (|S:=k,X:=2,Y:=3|)) = k
 * But be careful in (2) because of the extendibility of records.
 * - If S is a more-selector we have to make sure that the update on component
 *   X does not affect the selected subrecord.
 * - If X is a more-selector we have to make sure that S is not in the updated
 *   subrecord. 
 *)
val record_simproc =
  Simplifier.simproc (Theory.sign_of HOL.thy) "record_simp" ["s (u k r)"]
    (fn sg => fn _ => fn t =>
      (case t of (sel as Const (s, Type (_,[domS,rangeS]))) $ ((upd as Const (u, _)) $ k $ r) =>
        (case get_selectors sg s of Some () =>
          (case get_updates sg u of Some u_name =>
            let
              fun mk_abs_var x t = (x, fastype_of t);
              val {sel_upd={updates,...},extfields,...} = RecordsData.get_sg sg;
              fun flds T = 
                   foldl (fn (xs,(eN,_))=>xs@(map fst (Symtab.lookup_multi (extfields,eN))))
                         ([],(dest_recTs T));
              fun mk_eq_terms ((upd as Const (u,Type(_,[updT,_]))) $ k $ r) =
		  (case (Symtab.lookup (updates,u)) of
                     None => None
                   | Some u_name 
                     => if u_name = s
                        then let 
                               val rv = mk_abs_var "r" r
                               val rb = Bound 0
                               val kv = mk_abs_var "k" k
                               val kb = Bound 1 
                             in Some (upd$kb$rb,kb,[kv,rv],true) end
                        else if u_name mem (flds rangeS)
                             orelse s mem (flds updT)
                             then None
			     else (case mk_eq_terms r of 
                                     Some (trm,trm',vars,update_s) 
                                     => let   
					  val kv = mk_abs_var "k" k
                                          val kb = Bound (length vars)
		                        in Some (upd$kb$trm,trm',kv::vars,update_s) end
                                   | None
                                     => let 
					  val rv = mk_abs_var "r" r
                                          val rb = Bound 0
                                          val kv = mk_abs_var "k" k
                                          val kb = Bound 1 
                                        in Some (upd$kb$rb,rb,[kv,rv],false) end))
                | mk_eq_terms r = None     
            in
	      (case mk_eq_terms (upd$k$r) of
                 Some (trm,trm',vars,update_s) 
                 => if update_s 
		    then Some (prove_split_simp sg domS 
                                 (list_all(vars,(Logic.mk_equals (sel$trm,trm')))))
                    else Some (prove_split_simp sg domS 
                                 (list_all(vars,(Logic.mk_equals (sel$trm,sel$trm')))))
               | None => None)
            end
          | None => None)
        | None => None)
      | _ => None));

(* record_eq_simproc *)
(* looks up the most specific record-equality.
 * Note on efficiency:
 * Testing equality of records boils down to the test of equality of all components.
 * Therefore the complexity is: #components * complexity for single component.
 * Especially if a record has a lot of components it may be better to split up
 * the record first and do simplification on that (record_split_simp_tac).
 * e.g. r(|lots of updates|) = x
 *
 *               record_eq_simproc       record_split_simp_tac
 * Complexity: #components * #updates     #updates   
 *           
 *)
val record_eq_simproc =
  Simplifier.simproc (Theory.sign_of HOL.thy) "record_eq_simp" ["r = s"]
    (fn sg => fn _ => fn t =>
      (case t of Const ("op =", Type (_, [T, _])) $ _ $ _ =>
        (case rec_id T of
           "" => None
         | name => (case get_equalities sg name of
                                None => None
                              | Some thm => Some (thm RS Eq_TrueI)))
       | _ => None));


(* record_upd_simproc *)
(* simplify multiple updates; for example: "r(|M:=3,N:=1,M:=2,N:=4|) == r(|M:=2,N:=4|)" *)
val record_upd_simproc =
  Simplifier.simproc (Theory.sign_of HOL.thy) "record_upd_simp" ["(u1 k1 (u2 k2 r))"]
    (fn sg => fn _ => fn t =>
      (case t of ((upd as Const (u, Type(_,[_,Type(_,[T,_])]))) $ k $ r) =>
 	 let val {sel_upd={updates,...},...} = RecordsData.get_sg sg;
	     fun mk_abs_var x t = (x, fastype_of t);

             fun mk_updterm upds already ((upd as Const (u,_)) $ k $ r) =
		 if is_some (Symtab.lookup (upds,u))
		 then let 
			 fun rest already = mk_updterm upds already
		      in if is_some (Symtab.lookup (already,u)) 
			 then (case (rest already r) of
				 None => let 
				           val rv = mk_abs_var "r" r
                                           val rb = Bound 0
					   val kv = mk_abs_var "k" k
                                           val kb = Bound 1	      
                                         in Some (upd$kb$rb,rb,[kv,rv]) end
                               | Some (trm,trm',vars) 
				 => let 
				     val kv = mk_abs_var "k" k
                                     val kb = Bound (length vars)
                                    in Some (upd$kb$trm,trm',kv::vars) end)
	                 else (case rest (Symtab.update ((u,()),already)) r of 
				 None => None
		               | Some (trm,trm',vars) 
                                  => let
				      val kv = mk_abs_var "k" k
                                      val kb = Bound (length vars)
                                     in Some (upd$kb$trm,upd$kb$trm',kv::vars) end)
		     end
		 else None
	       | mk_updterm _ _ _ = None;

	 in (case mk_updterm updates Symtab.empty t of
	       Some (trm,trm',vars)
                => Some (prove_split_simp sg T  
                          (list_all(vars,(Logic.mk_equals (trm,trm')))))
             | None => None)
	 end
       | _ => None));

(* record_split_simproc *)
(* splits quantified occurrences of records, for which P holds. P can peek on the 
 * subterm starting at the quantified occurrence of the record (including the quantifier)
 *)
fun record_split_simproc P =
  Simplifier.simproc (Theory.sign_of HOL.thy) "record_split_simp" ["(a t)"]
    (fn sg => fn _ => fn t =>
      (case t of (Const (quantifier, Type (_, [Type (_, [T, _]), _])))$trm =>
         if quantifier = "All" orelse quantifier = "all" orelse quantifier = "Ex"
         then (case rec_id T of
                 "" => None
               | name
                  => if P t 
                     then (case get_splits sg name of
                             None => None
                           | Some (all_thm, All_thm, Ex_thm,_) 
                              => Some (case quantifier of
                                         "all" => all_thm
                                       | "All" => All_thm RS HOL.eq_reflection
                                       | "Ex"  => Ex_thm RS HOL.eq_reflection
                                       | _     => error "record_split_simproc"))
                     else None)
         else None
       | _ => None))

(* record_ex_sel_eq_simproc *)
(* simplifies: (EX s. x = sel s) resp. (EX s. sel s = x) to True *) 
val record_ex_sel_eq_simproc =
  Simplifier.simproc (Theory.sign_of HOL.thy) "record_ex_sel_eq_simproc" ["Ex t"]
    (fn sg => fn _ => fn t =>
       let fun prove prop = (quick_and_dirty_prove sg [] [] prop 
                             (fn _ => (simp_tac ((get_simpset sg) addsimps simp_thms
                                       addsimprocs [record_split_simproc (K true)]) 1)));
       in     
         (case t of 
           (Const ("Ex",Tex)$Abs(s,T,Const ("op =",Teq)$(Const (sel,Tsel)$Bound 0)$X)) =>
             (case get_selectors sg sel of Some () =>
                let 
                  val X' = ("x",range_type Tsel);
		  val prop = list_all ([X'], 
                               Logic.mk_equals
		                 (Const ("Ex",Tex)$Abs(s,T,Const ("op =",Teq)$
                                                      (Const (sel,Tsel)$Bound 0)$Bound 1),
                                  Const ("True",HOLogic.boolT)));
                in Some (prove prop) end
              | None => None)
          |(Const ("Ex",Tex)$Abs(s,T,Const ("op =",Teq)$X$(Const (sel,Tsel)$Bound 0))) =>
             (case get_selectors sg sel of Some () =>
                let 
                  val X' = ("x",range_type Tsel);
		  val prop = list_all ([X'], 
                               Logic.mk_equals
		                 (Const ("Ex",Tex)$Abs(s,T,Const ("op =",Teq)$
                                                     Bound 1$(Const (sel,Tsel)$Bound 0)),
                                  Const ("True",HOLogic.boolT)));
                in Some (prove prop) end 
            | None => None)
          | _ => None)
         end)


    

local
val inductive_atomize = thms "induct_atomize";
val inductive_rulify1 = thms "induct_rulify1";
in
(* record_split_simp_tac *)
(* splits (and simplifies) all records in the goal for which P holds. 
 * For quantified occurrences of a record
 * P can peek on the whole subterm (including the quantifier); for free variables P
 * can only peek on the variable itself. 
 *)
fun record_split_simp_tac P i st =
  let
    val sg = Thm.sign_of_thm st;
    val {sel_upd={simpset,...},...} 
            = RecordsData.get_sg sg;

    val has_rec = exists_Const
      (fn (s, Type (_, [Type (_, [T, _]), _])) =>
          (s = "all" orelse s = "All" orelse s = "Ex") andalso is_recT T 
        | _ => false);

    val goal = Library.nth_elem (i - 1, Thm.prems_of st);
    val frees = filter (is_recT o type_of) (term_frees goal);

    fun mk_split_free_tac free induct_thm i = 
	let val cfree = cterm_of sg free;
            val (_$(_$r)) = concl_of induct_thm;
            val crec = cterm_of sg r;
            val thm  = cterm_instantiate [(crec,cfree)] induct_thm;
        in EVERY [simp_tac (HOL_basic_ss addsimps inductive_atomize) i,
                  rtac thm i,
                  simp_tac (HOL_basic_ss addsimps inductive_rulify1) i]
	end;

    fun split_free_tac P i (free as Free (n,T)) = 
	(case rec_id T of
           "" => None
         | name => if P free 
                   then (case get_splits sg name of
                           None => None
                         | Some (_,_,_,induct_thm)
                             => Some (mk_split_free_tac free induct_thm i))
                   else None)
     | split_free_tac _ _ _ = None;

    val split_frees_tacs = mapfilter (split_free_tac P i) frees;
   
    val simprocs = if has_rec goal then [record_split_simproc P] else [];
   
  in st |> (EVERY split_frees_tacs) 
           THEN (Simplifier.full_simp_tac (simpset addsimprocs simprocs) i)
  end handle Library.LIST _ => Seq.empty;
end;


(* record_split_tac *)
(* splits all records in the goal, which are quantified by ! or !!. *)
fun record_split_tac i st =
  let
    val sg = Thm.sign_of_thm st;

    val has_rec = exists_Const
      (fn (s, Type (_, [Type (_, [T, _]), _])) =>
          (s = "all" orelse s = "All") andalso is_recT T 
        | _ => false);
 
    val goal = Library.nth_elem (i - 1, Thm.prems_of st);   

    fun is_all t =
      (case t of (Const (quantifier, _)$_) =>
         quantifier = "All" orelse quantifier = "all"
       | _ => false);
 
  in if has_rec goal 
     then Simplifier.full_simp_tac 
           (HOL_basic_ss addsimprocs [record_split_simproc is_all]) i st 
     else Seq.empty
  end handle Library.LIST _ => Seq.empty;

(* wrapper *)

val record_split_name = "record_split_tac";
val record_split_wrapper = (record_split_name, fn tac => record_split_tac ORELSE' tac);

(** theory extender interface **)

(* prepare arguments *)

(*note: read_raw_typ avoids expanding type abbreviations*)
fun read_raw_parent sign s =
  (case Sign.read_raw_typ (sign, K None) s handle TYPE (msg, _, _) => error msg of
    Type (name, Ts) => (Ts, name)
  | _ => error ("Bad parent record specification: " ^ quote s));

fun read_typ sign (env, s) =
  let
    fun def_sort (x, ~1) = assoc (env, x)
      | def_sort _ = None;
    val T = Type.no_tvars (Sign.read_typ (sign, def_sort) s) handle TYPE (msg, _, _) => error msg;
  in (Term.add_typ_tfrees (T, env), T) end;

fun cert_typ sign (env, raw_T) =
  let val T = Type.no_tvars (Sign.certify_typ sign raw_T) handle TYPE (msg, _, _) => error msg
  in (Term.add_typ_tfrees (T, env), T) end;

(* attributes *)

fun case_names_fields x = RuleCases.case_names ["fields"] x;
fun induct_type_global name = [case_names_fields, InductAttrib.induct_type_global name];
fun cases_type_global name = [case_names_fields, InductAttrib.cases_type_global name];

(* tactics *)

fun simp_all_tac ss simps = ALLGOALS (Simplifier.asm_full_simp_tac (ss addsimps simps));

(* do case analysis / induction according to rule on last parameter of ith subgoal 
 * (or on s if there are no parameters); 
 * Instatiation of record variable (and predicate) in rule is calculated to
 * avoid problems with higher order unification. 
 *)

fun try_param_tac s rule i st =
  let
    val cert = cterm_of (Thm.sign_of_thm st);
    val g = nth_elem (i - 1, prems_of st);
    val params = Logic.strip_params g;
    val concl = HOLogic.dest_Trueprop (Logic.strip_assums_concl g);
    val rule' = Thm.lift_rule (st, i) rule;
    val (P, ys) = strip_comb (HOLogic.dest_Trueprop
      (Logic.strip_assums_concl (prop_of rule')));
    (* ca indicates if rule is a case analysis or induction rule *)
    val (x, ca) = (case rev (drop (length params, ys)) of
        [] => (head_of (fst (HOLogic.dest_eq (HOLogic.dest_Trueprop
          (hd (rev (Logic.strip_assums_hyp (hd (prems_of rule')))))))), true)
      | [x] => (head_of x, false));
    val rule'' = cterm_instantiate (map (pairself cert) (case (rev params) of
        [] => (case assoc (map dest_Free (term_frees (prop_of st)), s) of
          None => sys_error "try_param_tac: no such variable"
        | Some T => [(P, if ca then concl else lambda (Free (s, T)) concl),
            (x, Free (s, T))])
      | (_, T) :: _ => [(P, list_abs (params, if ca then concl
          else incr_boundvars 1 (Abs (s, T, concl)))),
        (x, list_abs (params, Bound 0))])) rule'
  in compose_tac (false, rule'', nprems_of rule) i st end;

fun extension_typedef name repT alphas thy =
  let
    val UNIV = HOLogic.mk_UNIV repT;

    val (thy',{set_def=Some def, Abs_induct = abs_induct, 
               Abs_inject=abs_inject, Abs_inverse = abs_inverse,...}) =
        thy |> setmp TypedefPackage.quiet_mode true
           (TypedefPackage.add_typedef_i true None
             (suffix ext_typeN (Sign.base_name name), alphas, Syntax.NoSyn) UNIV None
             (Tactic.rtac UNIV_witness 1))
    val rewrite_rule = Tactic.rewrite_rule [def, rec_UNIV_I, rec_True_simp];
  in (thy',map rewrite_rule [abs_inject, abs_inverse, abs_induct])
  end;

fun extension_definition full name fields names alphas zeta moreT more vars thy = 
  let  
    val base = Sign.base_name;

    val fieldTs = (map snd fields);
    val alphas_zetaTs = map (fn n => TFree (n, HOLogic.typeS)) (alphas@[zeta]);
    val extT_name = suffix ext_typeN name
    val extT = Type (extT_name, alphas_zetaTs);
    val repT = foldr1 HOLogic.mk_prodT (fieldTs@[moreT]);
    val fields_more = fields@[(full moreN,moreT)];
    val bfields_more = map (apfst base) fields_more;
    val r = Free (rN,extT)
    val len = length fields;
    val idxms = 0 upto len;

    (* prepare declarations and definitions *)
    
    (*fields constructor*)
    val ext_decl = (mk_extC (name,extT) (fieldTs@[moreT]));     
    val ext_spec = Const ext_decl :== 
         (foldr (uncurry lambda) 
            (vars@[more],(mk_Abs name repT extT $ (foldr1 HOLogic.mk_prod (vars@[more]))))) 
    
    (*destructors*) 
    val dest_decls = map (mk_selC extT o (apfst (suffix ext_dest))) bfields_more;

    fun mk_dest_spec (i, (c,T)) =
      let val snds = (funpow i HOLogic.mk_snd (mk_Rep name repT extT $ r))
      in Const (mk_selC extT (suffix ext_dest c,T))
         :== (lambda r (if i=len then snds else HOLogic.mk_fst snds))
      end;
    val dest_specs =
      ListPair.map mk_dest_spec (idxms, fields_more);

    (* code generator data *)
        (* Representation as nested pairs is revealed for codegeneration *)
    val [rep_code,abs_code] = map (Codegen.parse_mixfix (K (Bound 0))) ["I","I"];
    val ext_type_code = Codegen.parse_mixfix (K dummyT) "_";
    
    (* 1st stage: defs_thy *)
    val (defs_thy, ([abs_inject, abs_inverse, abs_induct],ext_def::dest_defs)) =
        thy 
        |> extension_typedef name repT (alphas@[zeta])
        |>> Codegen.assoc_consts_i 
               [(mk_AbsN name,None,abs_code),
                (mk_RepN name,None,rep_code)]
        |>> Codegen.assoc_types [(extT_name,ext_type_code)]
        |>> Theory.add_consts_i (map Syntax.no_syn ((apfst base ext_decl)::dest_decls))
        |>>> PureThy.add_defs_i false (map Thm.no_attributes (ext_spec::dest_specs))

    
    (* prepare propositions *)

    val vars_more = vars@[more];
    val named_vars_more = (names@[full moreN])~~vars_more;
    val ext = list_comb (Const ext_decl,vars_more);
    val s     = Free (rN, extT);
    val P = Free (variant (map (fn (Free (x,_))=>x) vars_more) "P", extT-->HOLogic.boolT);
    val C = Free (variant (map (fn (Free (x,_))=>x) vars_more) "C", HOLogic.boolT);

    val inject_prop =
      let val vars_more' = map (fn (Free (x,T)) => Free (x ^ "'",T)) vars_more;
      in All (map dest_Free (vars_more@vars_more')) 
          ((HOLogic.eq_const extT $ 
            list_comb (Const ext_decl,vars_more)$list_comb (Const ext_decl,vars_more')) 
           ===
           foldr1 HOLogic.mk_conj (map HOLogic.mk_eq (vars_more ~~ vars_more')))
      end;

    val induct_prop =
      All (map dest_Free vars_more) (Trueprop (P $ ext)) ==> Trueprop (P $ s);
     
    val cases_prop =
      (All (map dest_Free vars_more) 
        (Trueprop (HOLogic.mk_eq (s,ext)) ==> Trueprop C)) 
      ==> Trueprop C;

    (*destructors*) 
    val dest_conv_props =
       map (fn (c, x as Free (_,T)) => mk_sel ext (suffix ext_dest c,T) === x) named_vars_more;

    val prove_standard = Tactic.prove_standard (Theory.sign_of defs_thy);
    fun prove_simp simps =
      let val tac = simp_all_tac HOL_ss simps
      in fn prop => prove_standard [] [] prop (K tac) end;
    
    (* prove propositions *)

    val inject = (prove_simp [ext_def,abs_inject,Pair_eq] inject_prop);

    val induct =
        prove_standard [] [] induct_prop (fn prems =>
         EVERY [try_param_tac rN abs_induct 1, 
                asm_full_simp_tac (HOL_ss addsimps [ext_def,split_paired_all]) 1]);

    val cases =
        prove_standard [] [] cases_prop (fn prems =>
         EVERY [asm_full_simp_tac (HOL_basic_ss addsimps [atomize_all, atomize_imp]) 1,
                try_param_tac rN induct 1,
                rtac impI 1,
                REPEAT (etac allE 1),
                etac mp 1,
                rtac refl 1])
	
    val dest_convs = map (prove_simp 
                           ([ext_def,abs_inverse]@Pair_sel_convs@dest_defs)) dest_conv_props;
    
    val (thm_thy,([inject',induct',cases'],[dest_convs'])) =
      defs_thy 
      |> (PureThy.add_thms o map Thm.no_attributes) 
           [("ext_inject", inject),
            ("ext_induct", induct),
            ("ext_cases", cases)]
      |>>> (PureThy.add_thmss o map Thm.no_attributes)
              [("dest_convs",dest_convs)] 

  in (thm_thy,extT,induct',inject',dest_convs')
  end;
   
fun chunks []      []   = []
  | chunks []      xs   = [xs]
  | chunks (l::ls) xs  = take (l,xs)::chunks ls (drop (l,xs));
 
fun chop_last [] = error "last: list should not be empty"
  | chop_last [x] = ([],x)
  | chop_last (x::xs) = let val (tl,l) = chop_last xs in (x::tl,l) end;
     	
fun subst_last s []      = error "subst_last: list should not be empty"
  | subst_last s ([x])   = [s]
  | subst_last s (x::xs) = (x::subst_last s xs);

(* mk_recordT builds up the record type from the current extension tpye extT and a list
 * of parent extensions, starting with the root of the record hierarchy 
*) 
fun mk_recordT extT parent_exts = 
    foldr (fn ((parent,Ts),T) => Type (parent, subst_last T Ts)) (parent_exts,extT);

(* record_definition *)

fun record_definition (args, bname) parent parents raw_fields thy = 
  let
    val sign = Theory.sign_of thy;

    val alphas = map fst args;
    val name = Sign.full_name sign bname;
    val full = Sign.full_name_path sign bname;
    val base = Sign.base_name;

    val (bfields, field_syntax) = split_list (map (fn (x, T, mx) => ((x, T), mx)) raw_fields);

    val parent_fields = flat (map #fields parents);
    val parent_chunks = map (length o #fields) parents;
    val parent_names = map fst parent_fields;
    val parent_types = map snd parent_fields;
    val parent_fields_len = length parent_fields;
    val parent_variants = variantlist (map base parent_names, [moreN, rN, rN ^ "'"]);
    val parent_vars = ListPair.map Free (parent_variants, parent_types);
    val parent_len = length parents;
    val parents_idx = (map #name parents) ~~ (0 upto (parent_len - 1));

    val fields = map (apfst full) bfields;
    val names = map fst fields;
    val extN = full bname;
    val types = map snd fields;