Cause #

My Firefox on NixOS met a problem: everytime the home environment is rebuilt, the ~/.mozilla folder must be removed for home-manager to set up configs. Therefore, all stored information, including those that cannot be generated from Nix like history, passwords, etc. are lost.

Blaming Nix for overriding those information is almost the sudden reaction. However, home-manager is just doing its job: reproduce the same thing. The problem is that we’re requiring something that should not be considered part of reproducibility - which is exactly the opposite.

Nix is just not for representing such information.

Static and Dynamic #

Intuitively, any thing contains both static and dynamic elements. Let’s first analyze some scenarios and divide them into these two parts, then summarize the composition of the concepts of static and dynamic, which are universal across different contexts, and explore why Nix greatly reflects these characteristics.

Runtime #

The general definition of Runtime refers to all things related to the running of an application. It is easily misunderstood that runtime is dynamic. It’s not true.

The environment of runtime can be static. All the runtime dependents required can be determined and pinned to a specific version in advance.

However, all the information collected along with the running and the dynamic adjustment of components like load balancer are obviously dynamic.

Development (Shell) #

Development shell requires a lot of static utilities. Tasks are required to run specific groups of commands to calculate some results. Services are required to be set up for running the application. This is why there’re CMake and alternatives like Just.

What about the dynamic ones? Well, actually, the code being developed is the dynamic part.

Browsing #

Let’s take Firefox for example. Firefox Sync provides a bunch of available things to be synced: bookmarks, search engines, passwords, history… The border can be vague - it really depends on your scenario. But, still, every scenario leads to two groups, not one, though groups can be empty.

To me, the first two are static and the rest are dynamic.

Conclusion #

The static is about the declaration and the definition which stay still along with time. For the static, changes are external. For the dynamic, however, changes are internal.

Obviously, the concepts of dynamic and static are relative. The same thing can be considered dynamic or static in different contexts.

Reflection by Nix #

Nix is a functional programming language. Once the expression is determined, the result is determined.¹ It’s considered statically naturally, since there’s no compile time or runtime for Nix.²

The lack of the stages mentioned above also indicates why Nix is not suitable for representing dynamic things. Nix is tailored for configuration. It’s for configuration, so it’s not used to build a web server or connect to a database. It does have the potential to do other things but why will we want such feature?

The different thing between Nix and other programming-like config languages such as Dhall is that it can also represent the blueprint of a package, which extends the range of the static things it can represent - the runnable thing is now static. Therefore, scenarios that treat packages/binaries as static things can now be defined in Nix.

What to Do with the Dynamic #

Define the tool that can handle it, using Nix. That’s it.

Examples are: Convert Nix to k8s manifast; config your system Git hosting platform; config your syncing account.