src/Pure/Isar/token.ML

       (Lexicon.scan_longid >> pair Long_Ident ||
         Lexicon.scan_id >> pair Ident ||
         Lexicon.scan_var >> pair Var ||
         Lexicon.scan_tid >> pair Type_Ident ||
         Lexicon.scan_tvar >> pair Type_Var ||
-        Lexicon.scan_float >> pair Float ||
-        Lexicon.scan_nat >> pair Nat ||
+        Symbol_Pos.scan_float >> pair Float ||
+        Symbol_Pos.scan_nat >> pair Nat ||
         scan_symid >> pair Sym_Ident) >> uncurry token));
 
 fun recover msg =
   (Symbol_Pos.recover_string_qq ||
     Symbol_Pos.recover_string_bq ||