I'm not sure what you mean by "nested function" as a cleanup mechanism, and couldn't find a mention of state machines for cleanup purposes either (but maybe I'm

I'm not sure what you mean by "nested function" as a cleanup mechanism, and couldn't find a mention of state machines for cleanup purposes either (but maybe I'm searching for the wrong keywords). Is there existing open source code where these can be found, or do you have a link to an explanation for these?