src/Pure/Syntax/parser.ML

                   in ((nt, (minPrec, [])) :: used, States') end);
 
             val dummy =
               if not (!warned) andalso
                  length (new_states @ States) > (!branching_level) then
-                (writeln "Warning: Currently parsed expression could be \
+                (warning "Currently parsed expression could be \
                          \extremely ambiguous.";
                  warned := true)
               else ();
           in
             processS used' (new_states @ States) (S :: Si, Sii)