Hacker News Reader

Comment by l0b0 | Hacker News Reader

At part 3 now, and it's great. I feel like I might finally learn what all the arcane stuff in the manuals actually mean. Most of the Nix documentation is like reading ASCII EBNF or research papers. This, on the other hand, has just the right amount of snark:

  >> A store path Q is reachable from another store path P if Q is in the closure of the references relation.
  >
  > Good definition. Intuitive term.

View on HN

I wasn't sure if this is supposed to be snarky, given the author said he has a background in functional programming and thus probably has a good understanding how closures are defined. The statement works both ways I suppose.

It's "closure" in the mathematical sense, not in the functionnal programming sense. It would have been clearer with the full term: "transitive closure" instead of just "closure".

> It's "closure" in the mathematical sense, not in the functionnal programming sense.

The latter being of course an instance of the former :) Your lambda uses a reference to a local variable `x`, so go follow it and transitively capture all its references, repeat until you've closed over all such transitions.

    let a = // whatever
    let b x = a + x;
    let f x = x + b x; // closes over b and transitively over a

Reply on news.ycombinator.com