# File recfun_codegen.ML

    (*  Title:      HOL/recfun_codegen.ML
        ID:         $Id: recfun_codegen.ML,v 1.17 2005/09/15 15:16:57 wenzelm Exp $
        Author:     Stefan Berghofer, TU Muenchen

    Code generator for recursive functions.
    *)

    signature RECFUN_CODEGEN =
    sig
      val add: string option -> theory attribute
      val del: theory attribute
      val setup: (theory -> theory) list
    end;

    structure RecfunCodegen : RECFUN_CODEGEN =
    struct

    open Codegen;

    structure CodegenData = TheoryDataFun
    (struct
      val name = "HOL/recfun_codegen";
      type T = (thm * string option) list Symtab.table;
      val empty = Symtab.empty;
      val copy = I;
      val extend = I;
      fun merge _ = Symtab.merge_multi' (Drule.eq_thm_prop o pairself fst);
      fun print _ _ = ();
    end);

    val dest_eqn = HOLogic.dest_eq o HOLogic.dest_Trueprop;
    val lhs_of = fst o dest_eqn o prop_of;
    val const_of = dest_Const o head_of o fst o dest_eqn;

    fun warn thm = warning ("RecfunCodegen: Not a proper equation:\n" ^
      string_of_thm thm);

    fun add optmod (p as (thy, thm)) =
      let
        val tab = CodegenData.get thy;
        val (s, _) = const_of (prop_of thm);
      in
        if Pattern.pattern (lhs_of thm) then
          (CodegenData.put (Symtab.update_multi (s, (thm, optmod)) tab) thy, thm)
        else (warn thm; p)
      end handle TERM _ => (warn thm; p);

    fun del (p as (thy, thm)) =
      let
        val tab = CodegenData.get thy;
        val (s, _) = const_of (prop_of thm);
      in case Symtab.lookup tab s of
          NONE => p
        | SOME thms => (CodegenData.put (Symtab.update (s,
            gen_rem (eq_thm o apfst fst) (thms, thm)) tab) thy, thm)
      end handle TERM _ => (warn thm; p);

    fun del_redundant thy eqs [] = eqs
      | del_redundant thy eqs (eq :: eqs') =
        let
          val matches = curry
            (Pattern.matches thy o pairself (lhs_of o fst))
        in del_redundant thy (eq :: eqs) (filter_out (matches eq) eqs') end;

    fun get_equations thy defs (s, T) =
      (case Symtab.lookup (CodegenData.get thy) s of
         NONE => ([], "")
       | SOME thms =>
           let val thms' = del_redundant thy []
             (List.filter (fn (thm, _) => is_instance thy T
               (snd (const_of (prop_of thm)))) thms)
           in if null thms' then ([], "")
             else (preprocess thy (map fst thms'),
               case snd (snd (split_last thms')) of
                   NONE => (case get_defn thy defs s T of
                       NONE => thyname_of_const s thy
                     | SOME ((_, (thyname, _)), _) => thyname)
                 | SOME thyname => thyname)
           end);

    fun mk_suffix thy defs (s, T) = (case get_defn thy defs s T of
      SOME (_, SOME i) => " def" ^ string_of_int i | _ => "");

    exception EQN of string * typ * string;

    fun cycle g (xs, x) =
      if x mem xs then xs
      else Library.foldl (cycle g) (x :: xs, List.concat (Graph.find_paths (fst g) (x, x)));

    fun add_rec_funs thy defs gr dep eqs module =
      let
        fun dest_eq t = (fst (const_of t) ^ mk_suffix thy defs (const_of t),
          dest_eqn (rename_term t));
        val eqs' = map dest_eq eqs;
        val (dname, _) :: _ = eqs';
        val (s, T) = const_of (hd eqs);

        fun mk_fundef module fname prfx gr [] = (gr, [])
          | mk_fundef module fname prfx gr ((fname', (lhs, rhs)) :: xs) =
          let
            val (gr1, pl) = invoke_codegen thy defs dname module false (gr, lhs);
            val (gr2, pr) = invoke_codegen thy defs dname module false (gr1, rhs);
            val (gr3, rest) = mk_fundef module fname' "and " gr2 xs
          in
            (gr3, Pretty.blk (4, [Pretty.str (if fname = fname' then "  | " else prfx),
               pl, Pretty.str " =", Pretty.brk 1, pr]) :: rest)
          end;

        fun put_code module fundef = map_node dname
          (K (SOME (EQN ("", dummyT, dname)), module, Pretty.string_of (Pretty.blk (0,
          separate Pretty.fbrk fundef @ [Pretty.str ";"])) ^ "\n\n"));

      in
        (case try (get_node gr) dname of
           NONE =>
             let
               val gr1 = add_edge (dname, dep)
                 (new_node (dname, (SOME (EQN (s, T, "")), module, "")) gr);
               val (gr2, fundef) = mk_fundef module "" "fun " gr1 eqs';
               val xs = cycle gr2 ([], dname);
               val cs = map (fn x => case get_node gr2 x of
                   (SOME (EQN (s, T, _)), _, _) => (s, T)
                 | _ => error ("RecfunCodegen: illegal cyclic dependencies:\n" ^
                    implode (separate ", " xs))) xs
             in (case xs of
                 [_] => (put_code module fundef gr2, module)
               | _ =>
                 if not (dep mem xs) then
                   let
                     val thmss as (_, thyname) :: _ = map (get_equations thy defs) cs;
                     val module' = if_library thyname module;
                     val eqs'' = map (dest_eq o prop_of) (List.concat (map fst thmss));
                     val (gr3, fundef') = mk_fundef module' "" "fun "
                       (add_edge (dname, dep)
                         (foldr (uncurry new_node) (del_nodes xs gr2)
                           (map (fn k =>
                             (k, (SOME (EQN ("", dummyT, dname)), module', ""))) xs))) eqs''
                   in (put_code module' fundef' gr3, module') end
                 else (gr2, module))
             end
         | SOME (SOME (EQN (_, _, s)), module', _) =>
             (if s = "" then
                if dname = dep then gr else add_edge (dname, dep) gr
              else if s = dep then gr else add_edge (s, dep) gr,
              module'))
      end;

    fun recfun_codegen thy defs gr dep module brack t = (case strip_comb t of
        (Const (p as (s, T)), ts) => (case (get_equations thy defs p, get_assoc_code thy s T) of
           (([], _), _) => NONE
         | (_, SOME _) => NONE
         | ((eqns, thyname), NONE) =>
            let
              val module' = if_library thyname module;
              val (gr', ps) = foldl_map
                (invoke_codegen thy defs dep module true) (gr, ts);
              val suffix = mk_suffix thy defs p;
              val (gr'', module'') =
                add_rec_funs thy defs gr' dep (map prop_of eqns) module';
              val (gr''', fname) = mk_const_id module'' (s ^ suffix) gr''
            in
              SOME (gr''', mk_app brack (Pretty.str (mk_qual_id module fname)) ps)
            end)
      | _ => NONE);

    val setup =
      [CodegenData.init,
       add_codegen "recfun" recfun_codegen,
       add_attribute ""
         (   Args.del |-- Scan.succeed del
          || Scan.option (Args.$$$ "target" |-- Args.colon |-- Args.name) >> add)];

    end;