SQL> declare
  2  cursor c is
  3  with
  4  function f1(a number) return number is begin return a; end;
  5  select f1(1) x from dual;
  6  begin
  7  open c;
  8  close c;
  9  end;
10  /
function f1(a number) return number is begin return a; end;
         *
ERROR at line 4:
ORA-06550: line 4, column 10:
PL/SQL: ORA-00905: missing keyword
ORA-06550: line 3, column 1:
PL/SQL: SQL Statement ignored
ORA-06550: line 4, column 56:
PLS-00103: Encountered the symbol "END" when expecting one of the following:
begin function pragma procedure subtype type <an identifier>
<a double-quoted delimited-identifier> current cursor delete
exists prior

SQL> with
  2  function f1(a number) return number is begin return a; end;
  3  select f1(1) x from dual;
  4  /

         X
----------
         1