rand-nix

RNG in Nix pure eval mode

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{
  pkgs,
}:

let
  #   pkgs = import <nixpkgs> { };

  genSeed =
    pkgs.runCommandLocal "recursive"
      {
        requiredSystemFeatures = [ "recursive-nix" ];
        buildInputs = [ pkgs.nix ];
      }
      ''
        cat $(nix-build -E 'let pkgs = import <nixpkgs> { }; in pkgs.runCommandLocal "your random number" { } "od -A n -t d -N 4 /dev/random > $out"') > $out
      '' |> builtins.readFile;

  #   mkGiantFile =
  #     pkgs.runCommand "evil evil evil" { } "${pkgs.util-linux}/bin/fallocate -l 1G $out" |> builtins.pathExists |> builtins.toString;
  #
  #   sleep = i:
  #     pkgs.runCommand ("sleeeeeep" + i) { } "sleep 10 && echo > $out" |> builtins.readFile;

  seed = genSeed; # + mkGiantFile + (sleep "a") +(sleep "b");

  hash = builtins.hashString "sha256";

  rng =
    seed:
    pkgs.lib.fix (self: {
      int = (builtins.fromTOML "x=0x${builtins.substring 28 8 (hash seed)}").x;

      intBetween = x: y: x + pkgs.lib.mod self.int (y - x);

      next = rng (hash seed);

      skip = pkgs.lib.flip pkgs.lib.pipe [
        (pkgs.lib.flip pkgs.lib.replicate (x: x.next))
        (pkgs.lib.pipe self)
      ];

      take = builtins.genList self.skip;
    });
in
(rng seed).int