With declarative programming, you describe the end result instead of the steps you want to execute to get that result. This means that you can execute your code as more times than you meant to without getting duplicate/incorrect output – that is, you get idempotentcy for free.

The description page for the #fosdem declarative programing page consists of 2 copies of the same paragraph; apparently someone accidentally uploaded it twice

…or has a *great* sense of humor

https://fosdem.org/2021/schedule/event/declarativeminimalistic/