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A (directed) graph is a set of nodes, connected by arrows (edges). The nodes and edges may contain data. Here are some graphs: All graphs made with graphviz (source) Graphs are ubiquitous in software engineering: Package dependencies form directed graphs, as do module imports. The internet is a graph of links between…
Take the following code: a = 1 a = a + 1 print(a) A common FP critique of imperative programming goes like this: “How can a = a + 1? That’s like saying 1 = 2. Mutable assignment makes no sense.” This is a notation mismatch: “equals” should mean “equality”, when it really means “assign”. I agree with this criticism and…
Disclaimer 2024-12-02 Since this rant is going viral again (again (again)), some disclaimers: I wrote this six years ago to “”“win”“” an ugly Twitter fight. I’m glad I anonymized the inciting tweet and hope I’m the only person still getting grief over this. The core interesting bit— why it’s mathematically valid to…
I saw this question on the Software Engineering Stack Exchange: What are the barriers that prevent widespread adoption of formal methods? The question was closed as opinion-based, and most of the answers were things like “its too expensive!!!” or “website isn’t airplane!!!” These are sorta kinda true but don’t explain…
People think it’s weird that I do all my development on a Windows machine. It’s definitely a second-class citizen experience in the wider development world, and Windows has a lot of really frustrating issues, but it’s still my favorite operating system. This is for exactly one reason: AutoHotKey. AHK is an engine for…
Picat is a research language intended to combine logic programming, imperative programming, and constraint solving. I originally learned it to help with vacation scheduling but soon discovered its planner module, which is one of the most fascinating programming models I’ve ever seen. First, a brief explanation of…
Let's make the CPython team regret adding pattern matching to Python!
Last year I got certified as an EMT. As part of the training I shadowed an ambulance for a day and assisted with each run. For each patient we treated, we had to fill out a patient care report. A patient care report. (source) EMTs are just one part in a long chain. If they transport a patient to a hospital, the…
tl;dr: online TLA+ manual/advanced techniques/examples here. TLA+ is a tool for testing abstract software designs. I first stumbled on it in 2016 and found it so useful I wrote a free online guide to help others learn it. Then I decided the guide wasn’t good enough and wrote Practical TLA+ in 2018. Then I decided the…
tl;dr annotated AHK scripts here. Anybody who’s spent time with me knows how much I love AutoHotKey, the flat-out best Windows automation tool in the world. Anybody’s who’s tried to use AutoHotKey knows how intimidating it can be. So to help with that, I’m sharing (almost) all of my scripts along with extensive…
This is part one of the Crossover Project. Part two is here and part three is here. A conference talk based on this work is now available here. I sat in front of Mat, idly chatting about tech and cuisine. Before now, I had known him mostly for his cooking pictures on Twitter, the kind that made me envious of…
A while back I wrote that Robert Martin was ruining software by being too good at programming. That was supposed to be a joke. Since then he’s done his damndest to actually ruin software by telling people they’re doing it wrong. His most recent response where he yells at software correctness was the breaking point for…
I’ve been using Vim for eight years and am still discovering new things. This is usually seen as a Good Thing About Vim. In my head, though, it’s a failing of discoverability: I keep discovering new things because Vim makes it so hard to know what’s available. While people often talk about the beauty of modal editing…
People say “Comments should explain why, not what.” I feel like starting a flame war today so I’m going to argue that comments should explain ‘what’ too. Please don’t use this as justification to write bad code, okay? Okay. First of all, why shouldn’t comments explain ‘what’? If you need comments to explain what’s…
Two universal facts about user documentation: Documentation is really important. We are really bad at writing it. We don’t have good theories on what makes for useful documentation. That is except for the four document model, or Diátaxis.1 I’m glad that people use it. I’m also a little frustrated that people use it…
I recently did a corporate TLA+ workshop and some people asked what TLA+ specs look like in practice. If you looked at the most common public examples, you’d probably come away thinking that people only used it for critical consensus algorithms. This is a problem for two reasons: first, it makes it harder to learn…
I really like decision tables but they’ve fallen out of common knowledge. Let’s fix that. A decision table is a means of concisely representing branching and conditional computations. In the most basic form, you have some columns that represent the “inputs” as booleans and some columns that represent outputs and…
Kenneth Iverson’s 1964 language, APL, won him the Turing Award. His award lecture, Notation as a Tool of Thought, argued that better notations would lead people to deeper insights about mathematics. He provided a number of examples ranging across linear algebra, arithmetic, probability, and logic. Unfortunately, most…
After my recent vitriol about unit testing, a couple of people sent me Why TDD is Crap as a thorough debunking of TDD and unit testing. As someone very interested in software correctness, I ended up writing a debunking of his debunking. Transcriptions will be in quotes, my responses below. Some important notes: From…
“Don’t write clever code.” Why not? “Because it’s hard to understand.” People who say this think of clever code such as Duff’s Device: Duff's Device send(to, from, count) registershort*to, *from; registercount; { registern =(count +7) /8; switch(count %8) { case0: do{ *to =*from++; case7: *to =*from++; case6: *to…
Functional programming and immutability are hot right now. On one hand, this is pretty great as there’s lots of nice things about functional programming. On the other hand, people get a little overzealous and start claiming that imperative code is unnatural or that purity is always preferable to mutation. I think that…
This is the companion reference for A Brief Introduction to Esoteric Languages, my lecture for a friend’s college class. The video should be legible to other viewers, and the material here should be (mostly) understandable without watching the video. The Esolangs Listed roughly in order of appearance in the talk, with…
In his book On War, Clausewitz defines friction as the difference between military theory and reality: Thus, then, in strategy everything is very simple, but not on that account very easy. Everything is very simple in war, but the simplest thing is difficult. These difficulties accumulate and produce a friction, which…
I love science. Not the “space is beautiful” faux-science, but the process of doing science. Hours spent calibrating equipment, cross-checking cites of cites of cites, tedious arguments about p-values and prediction intervals, all the stuff that makes science Go. And, when it does happen, the drama. I also want us to…
One day Alan Eliasen read a fart joke and got so mad he invented a programming language. 20 years later Frink is one of the best special purpose languages for dealing with units. “But why do we need a language just for dealing with units?” Glad you asked! Intro to Units A unit is the physical property a number…
Update 01/07/19 Greetings from 2019! The good news is that Chicago isn’t yet a radioactive crater. The bad news is almost everything I said about refinement in this article is wrong. I’m working on writing a more in-depth, rigorous treatment of refinement as its own article. But this one is currently explaining…
A couple years back I gave a talk on researching software history, using “linked list interview questions” as an example topic. Since referring people to a video is less accessible than just writing a blog post, I’ve reproduced the question here. So why do interviewers like to ask linked list questions? If you ask…
A common question I get about specs is how to model bad actors. Usually this is one of two contexts: The spec involves several interacting agents sharing a protocol, but some of the nodes are faulty or malicious: they will intentionally try to subvert the system. The spec involves an agent subject to outside forces…