SQL & PL/SQL

How can I query/access the source code of an anonymous block? For instance, if I want the source of a particular procedure, it's accessible from the "all_source" table. Even if it throws away the source for an anonymous block after it's done with it, it still needs to store it somewhere while it's parsing/executing, so it should at the very least be accessible within the scope of the block like so:

declare
    src_code varchar2;
begin
    select source
    into   src_code
    from   wherever the DB stores it;

    dbms_output.put_line(src_code);
end;