src/HOL/Nominal/nominal_fresh_fun.ML

generate_fresh works even if there is no free variable in the goal

(*  Title:      HOL/Nominal/nominal_fresh_fun.ML
    ID:         $Id$
    Authors:    Stefan Berghofer, Julien Narboux, TU Muenchen

A tactic to generate fresh names.
A tactic to get rid of the fresh_fun.
*)

(* First some functions that could be in the library *)

(* A tactical which applies a list of int -> tactic to the corresponding subgoals present after the application of another tactic. 
T THENL [A,B,C] is equivalent to T THEN (C 3 THEN B 2 THEN A 1) 
*)

infix 1 THENL

fun tac THENL tacs =
 tac THEN
  (EVERY (map  (fn (tac,i) => tac i) (rev tacs ~~ (length tacs downto 1))))

(* A tactical to test if a tactic completly solve a subgoal *)

fun SOLVEI t = t THEN_ALL_NEW (fn i => no_tac);

(* A version of TRY for int -> tactic *)

fun TRY' tac i =  TRY (tac i);

fun gen_res_inst_tac_term instf tyinst tinst elim th i st =
  let
    val thy = theory_of_thm st;
    val cgoal = nth (cprems_of st) (i - 1);
    val {maxidx, ...} = rep_cterm cgoal;
    val j = maxidx + 1;
    val tyinst' = map (apfst (Logic.incr_tvar j)) tyinst;
    val ps = Logic.strip_params (term_of cgoal);
    val Ts = map snd ps;
    val tinst' = map (fn (t, u) =>
      (head_of (Logic.incr_indexes (Ts, j) t),
       list_abs (ps, u))) tinst;
    val th' = instf
      (map (pairself (ctyp_of thy)) tyinst')
      (map (pairself (cterm_of thy)) tinst')
      (Thm.lift_rule cgoal th)
  in
    compose_tac (elim, th', nprems_of th) i st
  end handle Subscript => Seq.empty;

val res_inst_tac_term = 
  gen_res_inst_tac_term (curry Thm.instantiate);

val res_inst_tac_term' = 
  gen_res_inst_tac_term (K Drule.cterm_instantiate) [];

fun cut_inst_tac_term' tinst th =
  res_inst_tac_term' tinst false (Tactic.make_elim_preserve th);

fun get_dyn_thm thy name atom_name = (PureThy.get_thm thy (Name name)) handle _ => raise ERROR ("The atom type "^atom_name^" is not defined."); 

(* End of function waiting to be
 in the library *)

(* The theorems needed that are known at
compile time. *)

val at_exists_fresh' = thm "at_exists_fresh'";
val fresh_fun_app' = thm "fresh_fun_app'";
val fresh_prod = thm "fresh_prod";

(* A tactic to generate a name fresh for 
all the free variables and parameters of the goal *)

fun generate_fresh_tac atom_name i thm =
 let 
   val thy = theory_of_thm thm;
(* the parsing function returns a qualified name, we get back the base name *)
   val atom_basename = Sign.base_name atom_name;
   val goal = List.nth(prems_of thm, i-1);
   val ps = Logic.strip_params goal;
   val Ts = rev (map snd ps);
   fun is_of_fs_name T = Type.of_sort (Sign.tsig_of thy)
     (T, Sign.intern_sort thy ["fs_"^atom_basename]); 
(* rebuild de bruijn indices *)
   val bvs = map_index (Bound o fst) ps;
(* select variables of the right class *)
   val vs = filter (fn t => is_of_fs_name (fastype_of1 (Ts, t)))
     (term_frees goal @ bvs);
(* build the tuple *)
   val s = (Library.foldr1 (fn (v, s) =>
     HOLogic.pair_const (fastype_of1 (Ts, v)) (fastype_of1 (Ts, s)) $ v $ s) vs) handle _ => HOLogic.unit ;
   val fs_name_thm = get_dyn_thm thy ("fs_"^atom_basename^"1") atom_basename;
   val at_name_inst_thm = get_dyn_thm thy ("at_"^atom_basename^"_inst") atom_basename;
   val exists_fresh' = at_name_inst_thm RS at_exists_fresh';
(* find the variable we want to instantiate *)
   val x = hd (term_vars (prop_of exists_fresh'));
 in 
   (cut_inst_tac_term' [(x,s)] exists_fresh' 1 THEN
   rtac fs_name_thm 1 THEN
   etac exE 1) thm
  handle Empty  => all_tac thm (* if we collected no variables then we do nothing *)
  end;

fun get_inner_fresh_fun (Bound j) = NONE
  | get_inner_fresh_fun (v as Free _) = NONE 
  | get_inner_fresh_fun (v as Var _)  = NONE
  | get_inner_fresh_fun (Const _) = NONE
  | get_inner_fresh_fun (Abs (_, _, t)) = get_inner_fresh_fun t 
  | get_inner_fresh_fun (Const ("Nominal.fresh_fun",Type("fun",[Type ("fun",[Type (T,_),_]),_])) $ u) = SOME T 
  | get_inner_fresh_fun (t $ u) = 
     let val a = get_inner_fresh_fun u in
     if a = NONE then get_inner_fresh_fun t else a 
     end;

(* This tactic generates a fresh name 
of the atom type given by the inner most fresh_fun *)

fun generate_fresh_fun_tac i thm =
  let
    val goal = List.nth(prems_of thm, i-1);
    val atom_name_opt = get_inner_fresh_fun goal;
  in
  case atom_name_opt of 
    NONE => all_tac thm
  | SOME atom_name  => generate_fresh_tac atom_name i thm               
  end

(* Two substitution tactics which looks for the inner most occurence in 
   one assumption or in the conclusion *)

val search_fun     = curry (Seq.flat o (uncurry EqSubst.searchf_bt_unify_valid));
val search_fun_asm = EqSubst.skip_first_asm_occs_search EqSubst.searchf_bt_unify_valid;

fun subst_inner_tac           ctx = EqSubst.eqsubst_tac' ctx search_fun;
fun subst_inner_asm_tac_aux i ctx = EqSubst.eqsubst_asm_tac' ctx search_fun_asm i;

(* A tactic to substitute in the first assumption 
   which contains an occurence. *)

fun subst_inner_asm_tac ctx th =  curry (curry (FIRST' (map uncurry (map uncurry (map subst_inner_asm_tac_aux (1 upto Thm.nprems_of th)))))) ctx th;

fun fresh_fun_tac no_asm i thm = 
  (* Find the variable we instantiate *)
  let
    val thy = theory_of_thm thm;
    val ctx = Context.init_proof thy;
    val ss = simpset_of thy;
    val abs_fresh = PureThy.get_thms thy (Name "abs_fresh");
    val fresh_perm_app = PureThy.get_thms thy (Name "fresh_perm_app");
    val ss' = ss addsimps fresh_prod::abs_fresh;
    val ss'' = ss' addsimps fresh_perm_app;
    val x = hd (tl (term_vars (prop_of exI)));
    val goal = nth (prems_of thm) (i-1);
    val atom_name_opt = get_inner_fresh_fun goal;
    val n = List.length (Logic.strip_params goal);
    (* Here we rely on the fact that the variable introduced by generate_fresh_tac is the last one in the list, the inner one *)
  in
  case atom_name_opt of 
    NONE => all_tac thm
  | SOME atom_name  =>    
  let 
    val atom_basename = Sign.base_name atom_name;
    val pt_name_inst = get_dyn_thm thy ("pt_"^atom_basename^"_inst") atom_basename;
    val at_name_inst = get_dyn_thm thy ("at_"^atom_basename^"_inst") atom_basename;
    fun inst_fresh vars params i st =
   let val vars' = term_vars (prop_of st);
       val thy = theory_of_thm st;
   in case vars' \\ vars of 
     [x] => Seq.single (Thm.instantiate ([],[(cterm_of thy x,cterm_of thy (list_abs (params,Bound 0)))]) st)
    | _ => error "fresh_fun_simp: Too many variables, please report."
  end
  in
  ((fn st =>
  let 
    val vars = term_vars (prop_of st);
    val params = Logic.strip_params (nth (prems_of st) (i-1))
    (* The tactics which solve the subgoals generated 
       by the conditionnal rewrite rule. *)
    val post_rewrite_tacs =  
          [rtac pt_name_inst,
           rtac at_name_inst,
           TRY' (SOLVEI (NominalPermeq.finite_guess_tac ss'')),
           inst_fresh vars params THEN'
           (TRY' (SOLVEI (NominalPermeq.fresh_guess_tac ss''))) THEN'
           (TRY' (SOLVEI (asm_full_simp_tac ss'')))] 
  in 
   ((if no_asm then no_tac else
    (subst_inner_asm_tac ctx fresh_fun_app' i THENL post_rewrite_tacs)) 
    ORELSE
    (subst_inner_tac     ctx fresh_fun_app' i THENL post_rewrite_tacs)) st
  end)) thm
  
  end
  end

(* syntax for options, given "(no_asm)" will give back true, without
   gives back false *)
val options_syntax =
    (Args.parens (Args.$$$ "no_asm") >> (K true)) ||
     (Scan.succeed false);

val setup_generate_fresh =
  Method.goal_args_ctxt' Args.tyname (fn ctxt => generate_fresh_tac) 

val setup_fresh_fun_simp =
  Method.simple_args options_syntax 
  (fn b => fn _ => Method.SIMPLE_METHOD (fresh_fun_tac b 1))