src/HOL/Tools/BNF/bnf_fp_def_sugar.ML

 
 (* TODO: register "sum" and "prod" as datatypes to enable N2M reduction for them *)
 
 fun register_fp_sugar key fp_sugar =
   Local_Theory.declaration {syntax = false, pervasive = true}
-    (fn phi => Data.map (Symtab.update (key, morph_fp_sugar phi fp_sugar)));
+    (fn phi => Data.map (Symtab.default (key, morph_fp_sugar phi fp_sugar)));
 
 fun register_fp_sugars fp pre_bnfs nested_bnfs nesting_bnfs (fp_res as {Ts, ...}) ctr_defss
     ctr_sugars co_iterss mapss co_inducts co_iter_thmsss disc_co_itersss sel_co_iterssss lthy =
   (0, lthy)
   |> fold (fn T as Type (s, _) => fn (kk, lthy) => (kk + 1,