Writing a TLA⁺ tree-sitter grammar
My foray into free software
Posted on January 11, 2023
| Andrew Helwer
2021 saw the completion of my first substantial free software project: a TLA⁺ grammar for tree-sitter, the error-tolerant incremental parser generator. The project stabilized & found users over the course of 2022, then over the holidays I used it to build the TLA⁺ Unicode Converter. The new year is a time to reflect on the past and look to the future, so here in early 2023 seems ideal to publish my experience.
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What's the difference between a computer and a rock?
Posted on October 19, 2022
| Andrew Helwer
Author’s note: I wrote this in 2017 and it languished in the drafts since then because I couldn’t think of a good conclusion. Really this is typical of the subject matter and all this piece offers is something to chew on, if you have the interest in it or have never before considered the question. At the time I was helping tutor a TLA⁺ seminar and had the opportunity to ask Leslie Lamport (who has thought about computation quite a bit!
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The Missing Prelude to The Little Typer's Trickiest Chapter
Yes, it's the replace function in chapter 9
Posted on October 13, 2022
| Andrew Helwer
It’s hard to find a textbook series garnering more effusive praise than The Little Schemer, The Little Prover, The Little Typer & co. The Little Typer introduces dependent type theory and is the first of the series I’ve read. I quickly grew to appreciate & enjoy its dialogue-based presentation - I’m a real convert! I might release future didactic blog posts as a dialogue rather than straight recitation of material in block paragraphs.
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Regexes in the Z3 Theorem Prover
Analyzing Teleport RBAC
Posted on January 19, 2022
| Andrew Helwer
Republished from Teleport’s official blog (link). I received compensation from Teleport for writing this post.
Z3 is a satisfiability modulo theories (SMT) solver developed by Microsoft Research. With a description like that you’d expect it to be restricted to esoteric corners of the computerized mathematics world, but it’s made impressive inroads addressing conventional software engineering needs: analyzing network ACLs and firewalls in Microsoft Azure, for example. Z3 is used to answer otherwise-unanswerable questions like “are these two firewalls equivalent?
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Two pictures of quantum computation
Quantum interference in the sum-over-paths formalism
Posted on December 10, 2020
| Andrew Helwer
Interpretations of quantum mechanics are boring. Boring! Maybe the universe has a strict partition between quantum and non-quantum. Maybe there are a bunch of parallel universes with limited crosstalk. Or maybe it’s whatever the Bohmian mechanics people are talking about. Shut up and calculate, I think. I don’t say this out of some disdain for idle philosophizing or to put on airs of a salt-of-the-earth laborer in the equation mines. It’s just there are so, so many interesting things you can learn about in quantum theory without ever going near the interpretation question.
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How do you reason about a probabilistic distributed system?
Posted on September 11, 2020
| Andrew Helwer
In which I am stunted upon by coin flips Wasn’t too long ago that I felt pretty good about my knowledge of distributed systems. All someone really needed in order to understand them, I thought, was a thorough understanding of the paxos protocol and a willingness to reshape your brain in the image of TLA⁺. Maybe add a dash of conflict-free replicated datatypes, just so you know what “eventual consistency” means.
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Meditation
Sadly my only weapon against the attention economy
Posted on August 29, 2020
| Andrew Helwer
This isn’t going to be a post about how adopting a several-thousand-year-old practice can make you a better servant of capital. Instead, let’s talk about when I feel the lowest of the low. It comes after spending any number of hours on my computer, maybe even a full day, endlessly circling around different websites in search of stimulation, the quick jolt that comes with learning an interesting fact or watching a funny short video or seeing someone get dunked on for having a bad political opinion.
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Taking my home work setup seriously
Ergonomics & settling in for the long haul
Posted on August 14, 2020
(Last modified on January 23, 2022)
| Andrew Helwer
The headlines don’t lie. Microsoft, Google, Amazon, Facebook, and a whole host of other tech companies have announced employees will be working from home until early-mid 2021. There are reasons to believe this will be pushed back; even if the staggeringly ambitious timelines for vaccine development are met, a vaccine might not be a silver bullet and the pandemic could require management for the next 2-3 years. As a software engineer in big tech’s orbit, this means it’s time to settle in for the long haul and take my home work setup seriously.
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Doing a math assignment with the Lean theorem prover
Posted on April 5, 2020
| Andrew Helwer
Note: this post was written for Lean 3; the latest version, Lean 4, is a very different language.
Turn back the clock to 2009: a confused physics major newly infatuated with math and computer science, I enrolled in MATH 273: Numbers and Proofs at the University of Calgary. This wasn’t my first encounter with mathematical proof; in first-year calculus I’d mastered rote regurgitation of delta-epsilon proofs. Despite writing out several dozen, their meaning never progressed beyond a sort of incantation I can summon to this day (for every \( \epsilon > 0 \) there exists a \( \delta > 0 \) such that…).
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Simulating physical reality with a quantum computer
Quantum chemistry for complete beginners
Posted on December 21, 2019
| Andrew Helwer
Quantum Computers: Not Just for Breaking RSA There’s no denying it, Shor’s algorithm was a blockbuster result. The thought of an exotic new computer breaking all widely-used public-key crypto plays well with the public imagination, and so you’d be forgiven for believing quantum computing is ultimately a sort of billions-dollar make-work project for software engineers: forcing our profession to relive a Y2K-like mass upgrade of old systems to new, quantum-safe encryption algorithms.
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