File primrec_package.ML (Isabelle2005: October 2005)

# File primrec_package.ML

    (*  Title:      HOL/Tools/primrec_package.ML
        ID:         $Id: primrec_package.ML,v 1.52 2005/09/15 15:16:57 wenzelm Exp $
        Author:     Stefan Berghofer, TU Muenchen and Norbert Voelker, FernUni Hagen

    Package for defining functions on datatypes by primitive recursion.
    *)

    signature PRIMREC_PACKAGE =
    sig
      val quiet_mode: bool ref
      val add_primrec: string -> ((bstring * string) * Attrib.src list) list
        -> theory -> theory * thm list
      val add_primrec_i: string -> ((bstring * term) * theory attribute list) list
        -> theory -> theory * thm list
    end;

    structure PrimrecPackage : PRIMREC_PACKAGE =
    struct

    open DatatypeAux;

    exception RecError of string;

    fun primrec_err s = error ("Primrec definition error:\n" ^ s);
    fun primrec_eq_err sign s eq =
      primrec_err (s ^ "\nin\n" ^ quote (Sign.string_of_term sign eq));

    (* messages *)

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

    (* preprocessing of equations *)

    fun process_eqn sign (eq, rec_fns) =
      let
        val (lhs, rhs) =
    	if null (term_vars eq) then
    	    HOLogic.dest_eq (HOLogic.dest_Trueprop eq)
    	      handle TERM _ => raise RecError "not a proper equation"
    	else raise RecError "illegal schematic variable(s)";

        val (recfun, args) = strip_comb lhs;
        val fnameT = dest_Const recfun handle TERM _ =>
          raise RecError "function is not declared as constant in theory";

        val (ls', rest)  = take_prefix is_Free args;
        val (middle, rs') = take_suffix is_Free rest;
        val rpos = length ls';

        val (constr, cargs') = if null middle then raise RecError "constructor missing"
          else strip_comb (hd middle);
        val (cname, T) = dest_Const constr
          handle TERM _ => raise RecError "ill-formed constructor";
        val (tname, _) = dest_Type (body_type T) handle TYPE _ =>
          raise RecError "cannot determine datatype associated with function"

        val (ls, cargs, rs) = (map dest_Free ls',
    			   map dest_Free cargs',
    			   map dest_Free rs')
          handle TERM _ => raise RecError "illegal argument in pattern";
        val lfrees = ls @ rs @ cargs;

        fun check_vars _ [] = ()
          | check_vars s vars = raise RecError (s ^ commas_quote (map fst vars))
      in
        if length middle > 1 then
          raise RecError "more than one non-variable in pattern"
        else
         (check_vars "repeated variable names in pattern: " (duplicates lfrees);
          check_vars "extra variables on rhs: "
            (map dest_Free (term_frees rhs) \\ lfrees);
          case AList.lookup (op =) rec_fns fnameT of
            NONE =>
              (fnameT, (tname, rpos, [(cname, (ls, cargs, rs, rhs, eq))]))::rec_fns
          | SOME (_, rpos', eqns) =>
              if AList.defined (op =) eqns cname then
                raise RecError "constructor already occurred as pattern"
              else if rpos <> rpos' then
                raise RecError "position of recursive argument inconsistent"
              else
                AList.update (op =) (fnameT, (tname, rpos, (cname, (ls, cargs, rs, rhs, eq))::eqns))
                  rec_fns)
      end
      handle RecError s => primrec_eq_err sign s eq;

    fun process_fun sign descr rec_eqns ((i, fnameT as (fname, _)), (fnameTs, fnss)) =
      let
        val (_, (tname, _, constrs)) = List.nth (descr, i);

        (* substitute "fname ls x rs" by "y ls rs" for (x, (_, y)) in subs *)

        fun subst [] x = x
          | subst subs (fs, Abs (a, T, t)) =
              let val (fs', t') = subst subs (fs, t)
              in (fs', Abs (a, T, t')) end
          | subst subs (fs, t as (_ $ _)) =
              let val (f, ts) = strip_comb t;
              in
                if is_Const f andalso dest_Const f mem map fst rec_eqns then
                  let
                    val fnameT' as (fname', _) = dest_Const f;
                    val (_, rpos, _) = the (AList.lookup (op =) rec_eqns fnameT');
                    val ls = Library.take (rpos, ts);
                    val rest = Library.drop (rpos, ts);
                    val (x', rs) = (hd rest, tl rest)
                      handle Empty => raise RecError ("not enough arguments\
                       \ in recursive application\nof function " ^ quote fname' ^ " on rhs");
                    val (x, xs) = strip_comb x'
                  in
                    (case AList.lookup (op =) subs x of
                        NONE =>
                          let
                            val (fs', ts') = foldl_map (subst subs) (fs, ts)
                          in (fs', list_comb (f, ts')) end
                      | SOME (i', y) =>
                          let
                            val (fs', ts') = foldl_map (subst subs) (fs, xs @ ls @ rs);
                            val fs'' = process_fun sign descr rec_eqns ((i', fnameT'), fs')
                          in (fs'', list_comb (y, ts'))
                          end)
                  end
                else
                  let
                    val (fs', f'::ts') = foldl_map (subst subs) (fs, f::ts)
                  in (fs', list_comb (f', ts')) end
              end
          | subst _ x = x;

        (* translate rec equations into function arguments suitable for rec comb *)

        fun trans eqns ((cname, cargs), (fnameTs', fnss', fns)) =
          (case AList.lookup (op =) eqns cname of
              NONE => (warning ("No equation for constructor " ^ quote cname ^
                "\nin definition of function " ^ quote fname);
                  (fnameTs', fnss', (Const ("arbitrary", dummyT))::fns))
            | SOME (ls, cargs', rs, rhs, eq) =>
                let
                  val recs = List.filter (is_rec_type o snd) (cargs' ~~ cargs);
                  val rargs = map fst recs;
                  val subs = map (rpair dummyT o fst)
    		             (rev (rename_wrt_term rhs rargs));
                  val ((fnameTs'', fnss''), rhs') =
    		  (subst (map (fn ((x, y), z) =>
    			       (Free x, (body_index y, Free z)))
    			  (recs ~~ subs))
    		   ((fnameTs', fnss'), rhs))
                      handle RecError s => primrec_eq_err sign s eq
                in (fnameTs'', fnss'',
    		(list_abs_free (cargs' @ subs @ ls @ rs, rhs'))::fns)
                end)

      in (case AList.lookup (op =) fnameTs i of
          NONE =>
            if exists (equal fnameT o snd) fnameTs then
              raise RecError ("inconsistent functions for datatype " ^ quote tname)
            else
              let
                val (_, _, eqns) = the (AList.lookup (op =) rec_eqns fnameT);
                val (fnameTs', fnss', fns) = foldr (trans eqns)
                  ((i, fnameT)::fnameTs, fnss, []) constrs
              in
                (fnameTs', (i, (fname, #1 (snd (hd eqns)), fns))::fnss')
              end
        | SOME fnameT' =>
            if fnameT = fnameT' then (fnameTs, fnss)
            else raise RecError ("inconsistent functions for datatype " ^ quote tname))
      end;

    (* prepare functions needed for definitions *)

    fun get_fns fns (((i, (tname, _, constrs)), rec_name), (fs, defs)) =
      case AList.lookup (op =) fns i of
         NONE =>
           let
             val dummy_fns = map (fn (_, cargs) => Const ("arbitrary",
               replicate ((length cargs) + (length (List.filter is_rec_type cargs)))
                 dummyT ---> HOLogic.unitT)) constrs;
             val _ = warning ("No function definition for datatype " ^ quote tname)
           in
             (dummy_fns @ fs, defs)
           end
       | SOME (fname, ls, fs') => (fs' @ fs, (fname, ls, rec_name, tname)::defs);

    (* make definition *)

    fun make_def sign fs (fname, ls, rec_name, tname) =
      let
        val rhs = foldr (fn (T, t) => Abs ("", T, t))
    	            (list_comb (Const (rec_name, dummyT),
    				fs @ map Bound (0 ::(length ls downto 1))))
    		    ((map snd ls) @ [dummyT]);
        val defpair = (Sign.base_name fname ^ "_" ^ Sign.base_name tname ^ "_def",
    		   Logic.mk_equals (Const (fname, dummyT), rhs))
      in Theory.inferT_axm sign defpair end;

    (* find datatypes which contain all datatypes in tnames' *)

    fun find_dts (dt_info : datatype_info Symtab.table) _ [] = []
      | find_dts dt_info tnames' (tname::tnames) =
          (case Symtab.lookup dt_info tname of
              NONE => primrec_err (quote tname ^ " is not a datatype")
            | SOME dt =>
                if tnames' subset (map (#1 o snd) (#descr dt)) then
                  (tname, dt)::(find_dts dt_info tnames' tnames)
                else find_dts dt_info tnames' tnames);

    fun prepare_induct ({descr, induction, ...}: datatype_info) rec_eqns =
      let
        fun constrs_of (_, (_, _, cs)) =
          map (fn (cname:string, (_, cargs, _, _, _)) => (cname, map fst cargs)) cs;
        val params_of = these o AList.lookup (op =) (List.concat (map constrs_of rec_eqns));
      in
        induction
        |> RuleCases.rename_params (map params_of (List.concat (map (map #1 o #3 o #2) descr)))
        |> RuleCases.save induction
      end;

    fun add_primrec_i alt_name eqns_atts thy =
      let
        val (eqns, atts) = split_list eqns_atts;
        val sg = Theory.sign_of thy;
        val dt_info = DatatypePackage.get_datatypes thy;
        val rec_eqns = foldr (process_eqn sg) [] (map snd eqns);
        val tnames = distinct (map (#1 o snd) rec_eqns);
        val dts = find_dts dt_info tnames tnames;
        val main_fns =
    	map (fn (tname, {index, ...}) =>
    	     (index,
    	      fst (valOf (find_first (fn f => #1 (snd f) = tname) rec_eqns))))
    	dts;
        val {descr, rec_names, rec_rewrites, ...} =
    	if null dts then
    	    primrec_err ("datatypes " ^ commas_quote tnames ^
    			 "\nare not mutually recursive")
    	else snd (hd dts);
        val (fnameTs, fnss) = foldr (process_fun sg descr rec_eqns)
    	                       ([], []) main_fns;
        val (fs, defs) = foldr (get_fns fnss) ([], []) (descr ~~ rec_names);
        val defs' = map (make_def sg fs) defs;
        val nameTs1 = map snd fnameTs;
        val nameTs2 = map fst rec_eqns;
        val primrec_name =
          if alt_name = "" then (space_implode "_" (map (Sign.base_name o #1) defs)) else alt_name;
        val (thy', defs_thms') = thy |> Theory.add_path primrec_name |>
          (if eq_set (nameTs1, nameTs2) then (PureThy.add_defs_i false o map Thm.no_attributes) defs'
           else primrec_err ("functions " ^ commas_quote (map fst nameTs2) ^
             "\nare not mutually recursive"));
        val rewrites = (map mk_meta_eq rec_rewrites) @ defs_thms';
        val _ = message ("Proving equations for primrec function(s) " ^
          commas_quote (map fst nameTs1) ^ " ...");
        val simps = map (fn (_, t) => prove_goalw_cterm rewrites (cterm_of (Theory.sign_of thy') t)
            (fn _ => [rtac refl 1])) eqns;
        val (thy'', simps') = PureThy.add_thms ((map fst eqns ~~ simps) ~~ atts) thy';
        val thy''' = thy''
          |> (#1 o PureThy.add_thmss [(("simps", simps'),
               [Simplifier.simp_add_global, RecfunCodegen.add NONE])])
          |> (#1 o PureThy.add_thms [(("induct", prepare_induct (#2 (hd dts)) rec_eqns), [])])
          |> Theory.parent_path
      in
        (thy''', simps')
      end;

    fun add_primrec alt_name eqns thy =
      let
        val sign = Theory.sign_of thy;
        val ((names, strings), srcss) = apfst split_list (split_list eqns);
        val atts = map (map (Attrib.global_attribute thy)) srcss;
        val eqn_ts = map (fn s => term_of (Thm.read_cterm sign (s, propT))
          handle ERROR => error ("The error(s) above occurred for " ^ s)) strings;
        val rec_ts = map (fn eq => head_of (fst (HOLogic.dest_eq (HOLogic.dest_Trueprop eq)))
          handle TERM _ => primrec_eq_err sign "not a proper equation" eq) eqn_ts;
        val (_, eqn_ts') = InductivePackage.unify_consts (sign_of thy) rec_ts eqn_ts
      in
        add_primrec_i alt_name (names ~~ eqn_ts' ~~ atts) thy
      end;

    (* outer syntax *)

    local structure P = OuterParse and K = OuterKeyword in

    val primrec_decl =
      Scan.optional (P.$$$ "(" |-- P.name --| P.$$$ ")") "" --
        Scan.repeat1 (P.opt_thm_name ":" -- P.prop);

    val primrecP =
      OuterSyntax.command "primrec" "define primitive recursive functions on datatypes" K.thy_decl
        (primrec_decl >> (fn (alt_name, eqns) =>
          Toplevel.theory (#1 o add_primrec alt_name (map P.triple_swap eqns))));

    val _ = OuterSyntax.add_parsers [primrecP];

    end;

    end;