(*  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;