while i think that ansible is really cool, it's not the same as Nix.

correct me if i'm wrong, but afaik Ansible just modifies the current state of the System with a declarative configuration.

Nix reverts your system back to install and then applies the configuration. The result is that in Nix if i remove something from the configuration.nix it is as if it never existed, whereas on Ansible it stays unless i manually run a task to uninstall it.