nicer error message in case of duplicates

--- a/src/HOL/BNF/Tools/bnf_fp_def_sugar.ML	Tue Nov 05 15:30:53 2013 +1100
+++ b/src/HOL/BNF/Tools/bnf_fp_def_sugar.ML	Tue Nov 05 05:48:08 2013 +0100
@@ -1000,7 +1000,7 @@
 
     val qsoty = quote o Syntax.string_of_typ fake_lthy;
 
-    val _ = (case duplicates (op =) unsorted_As of [] => ()
+    val _ = (case Library.duplicates (op =) unsorted_As of [] => ()
       | A :: _ => error ("Duplicate type parameter " ^ qsoty A ^ " in " ^ co_prefix fp ^
           "datatype specification"));
 
@@ -1013,7 +1013,7 @@
 
     val mixfixes = map mixfix_of specs;
 
-    val _ = (case duplicates Binding.eq_name fp_bs of [] => ()
+    val _ = (case Library.duplicates Binding.eq_name fp_bs of [] => ()
       | b :: _ => error ("Duplicate type name declaration " ^ quote (Binding.name_of b)));
 
     val ctr_specss = map ctr_specs_of specs;

--- a/src/HOL/BNF/Tools/bnf_fp_n2m_sugar.ML	Tue Nov 05 15:30:53 2013 +1100
+++ b/src/HOL/BNF/Tools/bnf_fp_n2m_sugar.ML	Tue Nov 05 05:48:08 2013 +0100
@@ -97,7 +97,7 @@
 (* TODO: use right sorting order for "fp_sort" w.r.t. original BNFs (?) -- treat new variables
    as deads? *)
 fun mutualize_fp_sugars has_nested fp bs fpTs get_indices callssss fp_sugars0 no_defs_lthy0 =
-  if has_nested orelse has_duplicates (op =) fpTs then
+  if has_nested then
     let
       val thy = Proof_Context.theory_of no_defs_lthy0;
 
@@ -136,15 +136,15 @@
         |> mk_TFrees nn
         ||>> variant_tfrees fp_b_names;
 
-      fun freeze_fp_default (T as Type (s, Ts)) =
-          (case find_index (curry (op =) T) fpTs of
-            ~1 => Type (s, map freeze_fp_default Ts)
-          | kk => nth Xs kk)
-        | freeze_fp_default T = T;
-
       fun check_call_dead live_call call =
         if null (get_indices call) then () else incompatible_calls live_call call;
 
+      fun freeze_fp_simple (T as Type (s, Ts)) =
+          (case find_index (curry (op =) T) fpTs of
+            ~1 => Type (s, map freeze_fp_simple Ts)
+          | kk => nth Xs kk)
+        | freeze_fp_simple T = T;
+
       fun freeze_fp_map (callss, (live_call :: _, dead_calls)) s Ts =
         (List.app (check_call_dead live_call) dead_calls;
          Type (s, map2 freeze_fp (flatten_type_args_of_bnf (the (bnf_of no_defs_lthy s)) []
@@ -153,7 +153,7 @@
           (case map_partition (try (snd o dest_map no_defs_lthy s)) calls of
             ([], _) =>
             (case map_partition (try (snd o dest_abs_or_applied_map_or_ctr no_defs_lthy s)) calls of
-              ([], _) => freeze_fp_default T
+              ([], _) => freeze_fp_simple T
             | callsp => freeze_fp_map callsp s Ts)
           | callsp => freeze_fp_map callsp s Ts)
         | freeze_fp _ T = T;
@@ -257,6 +257,7 @@
     val qsoty = quote o Syntax.string_of_typ lthy;
     val qsotys = space_implode " or " o map qsoty;
 
+    fun duplicate_datatype T = error (qsoty T ^ " is not mutually recursive with itself");
     fun not_co_datatype0 T = error (qsoty T ^ " is not a " ^ co_prefix fp ^ "datatype");
     fun not_co_datatype (T as Type (s, _)) =
         if fp = Least_FP andalso
@@ -269,6 +270,8 @@
       error (qsotys Ts1 ^ " is neither mutually recursive with nor nested recursive via " ^
         qsotys Ts2);
 
+    val _ = (case Library.duplicates (op =) actual_Ts of [] => () | T :: _ => duplicate_datatype T);
+
     val perm_actual_Ts as Type (_, ty_args0) :: _ =
       sort (int_ord o pairself Term.size_of_typ) actual_Ts;