Comment by mrkeen

> databases are an example

Yes, it is possible because programmers have accepted the bargain that they must write purely-functional SQL.

Then the db is able to decide how best to optimise/apply/retry/copy-on-write/abort as necessary.

If SQL allowed you to directly mutate things, it would break everything. You couldn't 'LIMIT 10' if your loop might want to increment some data in row 40082.