void myfunc1()
{
    EXEC SQL create or replace
        function my_func (in_str IN varchar2)
        return date
        IS
        x date;
    BEGIN
    IF in_str IS NULL THEN
        x:  = NULL;
    ELSIF substr(in_str, 5,  1) = '-' THEN
    x := to_date(in_str, 'YYYY-MM-DD HH24:MI:SS');
    END IF;
    return x;
    END my_func;
    END-EXEC;
}