(*  Title:      HOL/Tools/recfun_codegen.ML

     ID:         $Id$

     Author:     Stefan Berghofer, TU Muenchen

 Code generator for recursive functions.

 *)

 signature RECFUN_CODEGEN =

 sig

   val add: string option -> attribute

   val del: attribute

   val setup: theory -> theory

 end;

 structure RecfunCodegen : RECFUN_CODEGEN =

 struct

 open Codegen;

 structure RecCodegenData = TheoryDataFun

 (

   type T = (thm * string option) list Symtab.table;

   val empty = Symtab.empty;

   val copy = I;

   val extend = I;

   fun merge _ = Symtab.merge_list (Thm.eq_thm_prop o pairself fst);

 );

 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 =

   let

     fun add thm =

       if Pattern.pattern (lhs_of thm) then

         RecCodegenData.map

           (Symtab.update_list ((fst o const_of o prop_of) thm, (thm, optmod)))

       else tap (fn _ => warn thm)

       handle TERM _ => tap (fn _ => warn thm);

   in

     Thm.declaration_attribute (fn thm => Context.mapping

       (add thm #> Code.add_func false thm) I)

   end;

 fun del_thm thm thy =

   let

     val tab = RecCodegenData.get thy;

     val (s, _) = const_of (prop_of thm);

   in case Symtab.lookup tab s of

       NONE => thy

     | SOME thms =>

         RecCodegenData.put (Symtab.update (s, remove (Thm.eq_thm o apsnd fst) thm thms) tab) thy

   end handle TERM _ => (warn thm; thy);

 val del = Thm.declaration_attribute

   (fn thm => Context.mapping (del_thm thm #> Code.del_func thm) I)

 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 (RecCodegenData.get thy) s of

      NONE => ([], "")

    | SOME thms => 

        let val thms' = del_redundant thy []

          (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 : string) =

   if member (op =) xs x then xs

   else Library.foldl (cycle g) (x :: xs, flat (Graph.all_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' : string, (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 =

   add_codegen "recfun" recfun_codegen

   #> Code.add_attribute ("", Args.del |-- Scan.succeed del

      || Scan.option (Args.$$$ "target" |-- Args.colon |-- Args.name) >> add);

 end;