7 Matching Annotations
1. Feb 2021
2. toraritte.github.io toraritte.github.io
1. A derivation from a Nix language view point is simply a set, with some attributes. Therefore you can pass the derivation around with variables like anything else.
2. the single repository technique. The natural implementation in Nix is to create a top-level Nix expression, and one expression for each package. The top-level expression imports and combines all expressions in a giant attribute set with name -> package pairs. But isn't that heavy? It isn't, because Nix is a lazy language, it evaluates only what's needed! And that's why nixpkgs is able to maintain such a big software repository in a giant attribute set.

This is the gist of how Nixpkgs works (and how it is organized).

3. 17.3. Fixed point

QUESTION: What is a fixed-point of a function?

ANSWER: See this video) at least, and the Fixed-point (mathematics)) wikipedia article:

In mathematics, a fixed point (sometimes shortened to fixpoint, also known as an invariant point) of a function is an element of the function's domain that is mapped to itself by the function. That is to say, c is a fixed point of the function `f` if `f(c) = c`. This means

``````f(f(...f(c)...)) = f n(c) = c
``````

an important terminating consideration when recursively computing f. A set of fixed points is sometimes called a fixed set.

For example, if f is defined on the real numbers by `f(x)=x^{2}-3x+4,}`, then 2 is a fixed point of `f`, because `f(2) = 2`.

There is also the wiki article fixed-point combinator that actually plays a role here, but read through the articles in this order.

Then dissect the Stackoverflow thread What is a Y combinator?, and pay attention to the comments! For example:

According to Mike Vanier's description, your definition for Y is actually not a combinator because it's recursive. Under "Eliminating (most) explicit recursion (lazy version)" he has the lazy scheme equivalent of your C# code but explains in point 2: "It is not a combinator, because the Y in the body of the definition is a free variable which is only bound once the definition is complete..." I think the cool thing about Y-combinators is that they produce recursion by evaluating the fixed-point of a function. In this way, they don't need explicit recursion. – GrantJ Jul 18 '11 at 0:02

(wut?)

Other resources in no particular order:

QUESTION: How the hell did they come up with the idea of using this with Nix and package management? (..and who? I remember a video saved somewhere, but maybe that was about overlays)

QUESTION: ... and how does it work in this context?

ANSWER: Well, not an answer yet, but this may be something in the right direction:

http://blog.tpleyer.de/posts/2020-01-29-Nix-overlay-evaluation-example.html

4. there's no ldconfig cache either. So where does bash find libc?

QUESTION: What is `ldconfig` cache?

QUESTION: What is `libc` and why does Bash need it?

5. Derivations/packages are stored in the Nix store as follows: /nix/store/hash-name, where the hash uniquely identifies the derivation (this isn't quite true, it's a little more complex), and the name is the name of the derivation.

QUESTION: So the Nix store houses derivations and not the built packages?

QUESTION: Are the hashes in the Nix store not unique?

6. In Nix there is the notion of a derivation rather than a package. The difference can be subtle at the beginning, so I will often use the words interchangeably.

Doesn't really say anything but thought it important to highlight this first mention of derivations in the Nix Pills.

7. From an administrator's point of view: you can use containers. The typical solution nowadays is to create a container per service, especially when different versions are needed. That somewhat solves the problem, but at a different level and with other drawbacks. For example, needing orchestration tools, setting up a shared cache of packages, and new machines to monitor rather than simple services.

This is a very good pointer; I guess it refers to systemd services when it mentions "simple services".