(*  Title:      HOL/recfun_codegen.ML

     ID:         $Id$

     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 get_rec_equations: theory -> string * typ -> (term list * term) list * typ

   val get_thm_equations: theory -> string * typ -> (thm list * typ) option

   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 get_rec_equations thy (s, T) =

   Symtab.lookup (CodegenData.get thy) s

   |> Option.map (fn thms => 

        List.filter (fn (thm, _) => is_instance thy T ((snd o const_of o prop_of) thm)) thms

        |> del_redundant thy [])

   |> Option.mapPartial (fn thms => if null thms then NONE else SOME thms)

   |> Option.map (fn thms =>

        (preprocess thy (map fst thms),

           (snd o const_of o prop_of o fst o hd) thms))

   |> the_default ([], dummyT)

   |> apfst (map prop_of)

   |> apfst (map (Codegen.rename_term #> HOLogic.dest_Trueprop #> HOLogic.dest_eq #> apfst (strip_comb #> snd)))

 fun get_thm_equations thy (c, ty) =

   Symtab.lookup (CodegenData.get thy) c

   |> Option.map (fn thms => 

        List.filter (fn (thm, _) => is_instance thy ty ((snd o const_of o prop_of) thm)) thms

        |> del_redundant thy [])

   |> Option.mapPartial (fn thms => if null thms then NONE else SOME thms)

   |> Option.map (fn thms =>

        (preprocess thy (map fst thms),

           (snd o const_of o prop_of o fst o hd) thms))

   |> (Option.map o apfst o map) (fn thm => thm RS HOL.eq_reflection);

 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),

   CodegenPackage.add_eqextr

     ("rec", fn thy => fn _ => get_thm_equations thy)

 ];

 end;