Comment by microtonal

This approach was already done by GoboLinux in 2005. And even GoboLinux was by far not the first - versioned AppDirs existed for a long time before; even perl stow enabled that. NixOS just uses a modified variant e. g. via hashed directory names. But I already adopted a similar scheme as GoboLinux did soon after I switched to Linux in 2005 (well 2004 but mostly 2005 as I was still a big noob in 2004 really).

Nix already existed in 2003. Besides that Nix store directories are more ingenious than versioned application directories (or hashed directories), the hash in the output path is the hash of the normalized derivation used to build the output path (well, in most cases, let's keep it simple). Derivations work similarly (also using hashes). Moreover, since a derivation can contain other derivations as an input, the Nix store represents hash/Merkle trees.

This makes it very powerful, because you can see which parts of the tree need to be rebuilt as a result of one derivation changing.

But with all its pros, the thing I hate by far the most in NixOS is .. nix.

I think it depends on your background. I did some Haskell at some point in my live and I like Nix. It is a very simple, clean, lazy, functional programming language. The primary thing I'm missing is static typing.

I instead opted for a less sophisticated solution in that ruby acts as the ultimate glue to whatever underlying operating system is used. What I would like is a NixOS variant that is simpler to use - and doesn't come with nix. Why can't I use ruby instead?

Because what nixpkgs does is not easily expressible/doable in Ruby. First, the package set is one huge expression in the end. That might seem weird, but it allows for a lot of powerful things like overlays. However, for performance reasons this requires lazy evaluation. Also other powerful abstractions require lazy evaluations (e.g. because there are some infinite recursions in nixpkgs).

Second, the Nix packaging model requires a purity (though this gap was only properly closed with flakes). You have to be able to rely on the fact that evaluating an expression evaluates to the same result. Otherwise a lot of things would break (like substitution from binary caches).

Third, things like overlays rely on fixed points, which can be done easily in a lazy functional language.

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Having used Nix for 8 years now, I have a long list of criticisms as well though :).