SQL & PL/SQL

What are the constraints when using mixed notation(named and positional) to invoke functions/procedures?

I have a procedure
Create or replace procedure test_proc2
(param1 in number,param2 in number ,param3 in number)
as
begin
DBMS_OUTPUT.PUT_LINE('Value of out parameter = ' || param1);
end test_proc;

I use the following methods to invoke the procedure


SQL> exec test_proc2(param1=>1,param2=>1,param3=>1);--Named notation

PL/SQL procedure successfully completed.

SQL> exec(1,param2=>1,param3=>1);--Mixed Notation
BEGIN (1,param2=>1,param3=>1); END;

*
ERROR at line 1:
ORA-06550: line 1, column 7:
PLS-00103: Encountered the symbol "(" when expecting one of the following:

How can I use mixed notation in the case described above?

Thanks in advance
Ann