src/ZF/Tools/datatype_package.ML

   (** Generating function variables for the case definition
       Non-identifiers (e.g. infixes) get a name of the form f_op_nnn. **)
 
   (*The function variable for a single constructor*)
   fun add_case ((_, T, _), name, args, _) (opno, cases) =
-    if Syntax.is_identifier name then
+    if Lexicon.is_identifier name then
       (opno, (Free (case_varname ^ "_" ^ name, T), args) :: cases)
     else
       (opno + 1, (Free (case_varname ^ "_op_" ^ string_of_int opno, T), args)
        :: cases);