Town of ZZT - Remixed

TL;DR: ZZT is now 30, there’s still a community, we’ve remixed the shareware world, it’s pretty fun, and you can play it online.

Thirty years ago, on the 15th of January 1991, Tim Sweeney released his first game to the world: a little arcadey game called ZZT, for the IBM PC and compatibles.

Vaccine Deployment

TL;DR: Despite earlier reservations, I will probably be taking a vaccine when offered, but it would be for different reasons if I was outside Australia. Also, continue to watch out for manipulation and fudging from authorities.

(Note: Twitter links have screenshots next to them, as it’s notoriously difficult to predict what Twitter shows on the other end of a link.)

Emergency approvals for the major vaccine candidates (Pfizer/BioNTech, Moderna, Oxford/AstraZeneca) have been issued, and it’s time to scale up and deploy. Then we reach herd immunity and get back to normal life, right? Well, first we need to make sure we’re all talking about the same “herd immunity”, and watch closely for shifting definitions. Between November and December 2020, the WHO’s website changed its definition of “herd immunity” at least twice (emphasis in the quotes is mine):

Profunctor Decoders? Optical Decoders?

I’ve been wrangling with an interesting decoding problem over the weekend. I started out fiddling with profunctors and arrows, but it morphed into something more lenslike for a while. Since Chris Penner has just published his article about fitting Witherable into an optical framework, I thought I’d write up what I have so far, and see if I can get some useful thoughts out while this stuff is flavour of the week.

Accidentally-Quadratic HashMaps

TL;DR: Unless you’re careful, using foldMap to build HashMaps (from unordered-containers) can take O(n²) time. This can be avoided by:

1. Building a Map (from containers) instead;

2. Using foldr or foldl with insert; or

3. Using foldMap to build an intermediate list [(k, v)] and then building the HashMap with fromList.

Shout-out to Luke Worth who found this out while we were chasing down performance problems.

Building and Importing NixOS AMIs on EC2

Update (2020-09-03): /u/zimbatm on lobste.rs suggested the nixos-generators project. Added link and brief discussion.

Update (2020-11-29): Added notes on the impact of instance limits on Packer builds.

The NixOS project publishes Amazon Machine Images (AMIs) that are a great base for reproducible servers. This post describes how NixOS and EC2 work together, first showing how to build upon the NixOS project’s public AMIs; and then digging all the way into the scripts maintainers use to build, import and distribute new AMIs on AWS.

Getting a NixOS AMI

There are few good ways to get AMI IDs for NixOS project images:

• The NixOS project publishes its images with owner-id=080433136561; you can use this with an aws ec2 describe-images call. jq is a good way to select the interesting parts of the response, and is the easiest way to find an AArch64 (which AWS calls arm64) AMI:

  # Return the most recent AArch64 NixOS image in the region
  $ aws ec2 describe-images \
      --region ap-southeast-2 \
      --filters Name=owner-id,Values=080433136561 \
    | jq '.Images | map(select(.Architecture == "arm64")) | sort_by(.CreationDate) | reverse | map({ ImageId, Description }) | .[0]'
  {
    "ImageId": "ami-05446a2f818cd3263",
    "Description": "NixOS 20.03.2351.f8248ab6d9e aarch64-linux"
  }

• The NixOS download page lists AMI IDs for the most recent stable release, which I think are all x86_64 images. Scroll down to the “Getting NixOS” section and click the “Amazon EC2” tab to find a list of AMIs, one for each region. The launch buttons take you straight to the launch wizard in the EC2 Management Console.

• There is a list of AMIs going back to NixOS 14.04 in <nixpkgs/nixos/modules/virtualisation/ec2-amis.nix>. You can retrieve a specific AMI ID with a nix command like:

  $ nix eval --raw '(import <nixpkgs/nixos/modules/virtualisation/ec2-amis.nix>)."20.03".ap-southeast-2.hvm-ebs'
  ami-04c0f3a75f63daddd