File datatype_realizer.ML (Isabelle2005: October 2005)

# File datatype_realizer.ML

    (*  Title:      HOL/Tools/datatype_realizer.ML
        ID:         $Id: datatype_realizer.ML,v 1.12 2005/09/20 14:17:34 haftmann Exp $
        Author:     Stefan Berghofer, TU Muenchen

    Porgram extraction from proofs involving datatypes:
    Realizers for induction and case analysis
    *)

    signature DATATYPE_REALIZER =
    sig
      val add_dt_realizers: (string * sort) list ->
        DatatypeAux.datatype_info list -> theory -> theory
    end;

    structure DatatypeRealizer : DATATYPE_REALIZER =
    struct

    open DatatypeAux;

    fun subsets i j = if i <= j then
           let val is = subsets (i+1) j
           in map (fn ks => i::ks) is @ is end
         else [[]];

    fun forall_intr_prf (t, prf) =
      let val (a, T) = (case t of Var ((a, _), T) => (a, T) | Free p => p)
      in Abst (a, SOME T, Proofterm.prf_abstract_over t prf) end;

    fun prf_of thm =
      let val {sign, prop, der = (_, prf), ...} = rep_thm thm
      in Reconstruct.reconstruct_proof sign prop prf end;

    fun prf_subst_vars inst =
      Proofterm.map_proof_terms (subst_vars ([], inst)) I;

    fun is_unit t = snd (strip_type (fastype_of t)) = HOLogic.unitT;

    fun tname_of (Type (s, _)) = s
      | tname_of _ = "";

    fun mk_realizes T = Const ("realizes", T --> HOLogic.boolT --> HOLogic.boolT);

    fun make_ind sorts ({descr, rec_names, rec_rewrites, induction, ...} : datatype_info) (is, thy) =
      let
        val sg = sign_of thy;
        val recTs = get_rec_types descr sorts;
        val pnames = if length descr = 1 then ["P"]
          else map (fn i => "P" ^ string_of_int i) (1 upto length descr);

        val rec_result_Ts = map (fn ((i, _), P) =>
          if i mem is then TFree ("'" ^ P, HOLogic.typeS) else HOLogic.unitT)
            (descr ~~ pnames);

        fun make_pred i T U r x =
          if i mem is then
            Free (List.nth (pnames, i), T --> U --> HOLogic.boolT) $ r $ x
          else Free (List.nth (pnames, i), U --> HOLogic.boolT) $ x;

        fun mk_all i s T t =
          if i mem is then list_all_free ([(s, T)], t) else t;

        val (prems, rec_fns) = split_list (List.concat (snd (foldl_map
          (fn (j, ((i, (_, _, constrs)), T)) => foldl_map (fn (j, (cname, cargs)) =>
            let
              val Ts = map (typ_of_dtyp descr sorts) cargs;
              val tnames = variantlist (DatatypeProp.make_tnames Ts, pnames);
              val recs = List.filter (is_rec_type o fst o fst) (cargs ~~ tnames ~~ Ts);
              val frees = tnames ~~ Ts;

              fun mk_prems vs [] =
                    let
                      val rT = List.nth (rec_result_Ts, i);
                      val vs' = filter_out is_unit vs;
                      val f = mk_Free "f" (map fastype_of vs' ---> rT) j;
                      val f' = Pattern.eta_contract (list_abs_free
                        (map dest_Free vs, if i mem is then list_comb (f, vs')
                          else HOLogic.unit));
                    in (HOLogic.mk_Trueprop (make_pred i rT T (list_comb (f, vs'))
                      (list_comb (Const (cname, Ts ---> T), map Free frees))), f')
                    end
                | mk_prems vs (((dt, s), T) :: ds) =
                    let
                      val k = body_index dt;
                      val (Us, U) = strip_type T;
                      val i = length Us;
                      val rT = List.nth (rec_result_Ts, k);
                      val r = Free ("r" ^ s, Us ---> rT);
                      val (p, f) = mk_prems (vs @ [r]) ds
                    in (mk_all k ("r" ^ s) (Us ---> rT) (Logic.mk_implies
                      (list_all (map (pair "x") Us, HOLogic.mk_Trueprop
                        (make_pred k rT U (app_bnds r i)
                          (app_bnds (Free (s, T)) i))), p)), f)
                    end

            in (j + 1,
              apfst (curry list_all_free frees) (mk_prems (map Free frees) recs))
            end) (j, constrs)) (1, descr ~~ recTs))));

        fun mk_proj j [] t = t
          | mk_proj j (i :: is) t = if null is then t else
              if j = i then HOLogic.mk_fst t
              else mk_proj j is (HOLogic.mk_snd t);

        val tnames = DatatypeProp.make_tnames recTs;
        val fTs = map fastype_of rec_fns;
        val ps = map (fn ((((i, _), T), U), s) => Abs ("x", T, make_pred i U T
          (list_comb (Const (s, fTs ---> T --> U), rec_fns) $ Bound 0) (Bound 0)))
            (descr ~~ recTs ~~ rec_result_Ts ~~ rec_names);
        val r = if null is then Extraction.nullt else
          foldr1 HOLogic.mk_prod (List.mapPartial (fn (((((i, _), T), U), s), tname) =>
            if i mem is then SOME
              (list_comb (Const (s, fTs ---> T --> U), rec_fns) $ Free (tname, T))
            else NONE) (descr ~~ recTs ~~ rec_result_Ts ~~ rec_names ~~ tnames));
        val concl = HOLogic.mk_Trueprop (foldr1 (HOLogic.mk_binop "op &")
          (map (fn ((((i, _), T), U), tname) =>
            make_pred i U T (mk_proj i is r) (Free (tname, T)))
              (descr ~~ recTs ~~ rec_result_Ts ~~ tnames)));
        val cert = cterm_of sg;
        val inst = map (pairself cert) (map head_of (HOLogic.dest_conj
          (HOLogic.dest_Trueprop (concl_of induction))) ~~ ps);

        val thm = simple_prove_goal_cterm (cert (Logic.list_implies (prems, concl)))
          (fn prems =>
             [rewrite_goals_tac (map mk_meta_eq [fst_conv, snd_conv]),
              rtac (cterm_instantiate inst induction) 1,
              ALLGOALS ObjectLogic.atomize_tac,
              rewrite_goals_tac (o_def :: map mk_meta_eq rec_rewrites),
              REPEAT ((resolve_tac prems THEN_ALL_NEW (fn i =>
                REPEAT (etac allE i) THEN atac i)) 1)]);

        val ind_name = Thm.name_of_thm induction;
        val vs = map (fn i => List.nth (pnames, i)) is;
        val (thy', thm') = thy
          |> Theory.absolute_path
          |> PureThy.store_thm
            ((space_implode "_" (ind_name :: vs @ ["correctness"]), thm), [])
          |>> Theory.restore_naming thy;

        val ivs = Drule.vars_of_terms
          [Logic.varify (DatatypeProp.make_ind [descr] sorts)];
        val rvs = Drule.vars_of_terms [prop_of thm'];
        val ivs1 = map Var (filter_out (fn (_, T) =>
          tname_of (body_type T) mem ["set", "bool"]) ivs);
        val ivs2 = map (fn (ixn, _) => Var (ixn, valOf (AList.lookup (op =) rvs ixn))) ivs;

        val prf = foldr forall_intr_prf
         (foldr (fn ((f, p), prf) =>
            (case head_of (strip_abs_body f) of
               Free (s, T) =>
                 let val T' = Type.varifyT T
                 in Abst (s, SOME T', Proofterm.prf_abstract_over
                   (Var ((s, 0), T')) (AbsP ("H", SOME p, prf)))
                 end
             | _ => AbsP ("H", SOME p, prf)))
               (Proofterm.proof_combP
                 (prf_of thm', map PBound (length prems - 1 downto 0))) (rec_fns ~~ prems_of thm)) ivs2;

        val r' = if null is then r else Logic.varify (foldr (uncurry lambda)
          r (map Logic.unvarify ivs1 @ filter_out is_unit
              (map (head_of o strip_abs_body) rec_fns)));

      in Extraction.add_realizers_i [(ind_name, (vs, r', prf))] thy' end;

    fun make_casedists sorts ({index, descr, case_name, case_rewrites, exhaustion, ...} : datatype_info, thy) =
      let
        val sg = sign_of thy;
        val cert = cterm_of sg;
        val rT = TFree ("'P", HOLogic.typeS);
        val rT' = TVar (("'P", 0), HOLogic.typeS);

        fun make_casedist_prem T (cname, cargs) =
          let
            val Ts = map (typ_of_dtyp descr sorts) cargs;
            val frees = variantlist
              (DatatypeProp.make_tnames Ts, ["P", "y"]) ~~ Ts;
            val free_ts = map Free frees;
            val r = Free ("r" ^ NameSpace.base cname, Ts ---> rT)
          in (r, list_all_free (frees, Logic.mk_implies (HOLogic.mk_Trueprop
            (HOLogic.mk_eq (Free ("y", T), list_comb (Const (cname, Ts ---> T), free_ts))),
              HOLogic.mk_Trueprop (Free ("P", rT --> HOLogic.boolT) $
                list_comb (r, free_ts)))))
          end;

        val SOME (_, _, constrs) = AList.lookup (op =) descr index;
        val T = List.nth (get_rec_types descr sorts, index);
        val (rs, prems) = split_list (map (make_casedist_prem T) constrs);
        val r = Const (case_name, map fastype_of rs ---> T --> rT);

        val y = Var (("y", 0), Type.varifyT T);
        val y' = Free ("y", T);

        val thm = prove_goalw_cterm [] (cert (Logic.list_implies (prems,
          HOLogic.mk_Trueprop (Free ("P", rT --> HOLogic.boolT) $
            list_comb (r, rs @ [y'])))))
          (fn prems =>
             [rtac (cterm_instantiate [(cert y, cert y')] exhaustion) 1,
              ALLGOALS (EVERY'
                [asm_simp_tac (HOL_basic_ss addsimps case_rewrites),
                 resolve_tac prems, asm_simp_tac HOL_basic_ss])]);

        val exh_name = Thm.name_of_thm exhaustion;
        val (thy', thm') = thy
          |> Theory.absolute_path
          |> PureThy.store_thm ((exh_name ^ "_P_correctness", thm), [])
          |>> Theory.restore_naming thy;

        val P = Var (("P", 0), rT' --> HOLogic.boolT);
        val prf = forall_intr_prf (y, forall_intr_prf (P,
          foldr (fn ((p, r), prf) =>
            forall_intr_prf (Logic.varify r, AbsP ("H", SOME (Logic.varify p),
              prf))) (Proofterm.proof_combP (prf_of thm',
                map PBound (length prems - 1 downto 0))) (prems ~~ rs)));
        val r' = Logic.varify (Abs ("y", Type.varifyT T,
          list_abs (map dest_Free rs, list_comb (r,
            map Bound ((length rs - 1 downto 0) @ [length rs])))));

      in Extraction.add_realizers_i
        [(exh_name, (["P"], r', prf)),
         (exh_name, ([], Extraction.nullt, prf_of exhaustion))] thy'
      end;

    fun add_dt_realizers sorts infos thy = if !proofs < 2 then thy else
      (message "Adding realizers for induction and case analysis ..."; thy
       |> curry (Library.foldr (make_ind sorts (hd infos)))
         (subsets 0 (length (#descr (hd infos)) - 1))
       |> curry (Library.foldr (make_casedists sorts)) infos);

    end;