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My job these days is teaching TLA+ and formal methods: specifying designs to find bugs in them. But just knowing the syntax isn’t enough to write specs, and it helps to have examples to draw from. I recently read Chris Siebenmann’s Even in Go, concurrency is still not easy and thought it would make a good case study…
Graphing TLA+ state spaces for fun and profit.
img {border-style: groove; border-width: 1px;} I love Autohotkey so much that it keeps me on Windows. It’s the best GUI automation tool out there. Here’s a shortcut that opens my current browser tab in the Wayback Machine: #HotIf WinActive("ahk_exe firefox.exe") >!^s:: { Keywait("RControl") Keywait("RAlt")…
This is part one of a two-part article. Part two is here. A while back somebody told me to check out MiniZinc. Eventually I did and really enjoyed it, so figured I’d write about it here. This is actually going to be a two part article. Right now we’re talking about what it is and how it works, and in the next post…
A common assumption I see on the ‘net is that NP-complete problems are impossible to solve. I recently read that dependency management in Python is hard because package resolution is NP-complete. This is true in principle, but the reality is more complicated. When we say “NP-complete is hard” we’re talking about…
This is an “intro packet” you can use to argue for the benefits of formal methods (FM) to your boss. It’s a short explanation, a list of benefits and case studies, and a demo. Everything’s in TLA+, but the arguments apply equally well to Alloy, B, statecharts, etc. Adapt the material to your specific needs. Quick…
Decision tables are easy, simple, and powerful. You can teach them in five minutes and write one in half that time. You can look at a table and understand what it’s saying, see if it matches your problem, and check for design flaws. So it’s kinda weird that there’s basically nothing about them online. I wrote an…
I really like the c2 wiki as a historical artifact: a lot of big names in Agile and Extreme Programming argued with each other there.1 One thing they did was the Extreme Programming Challenge, where people tried to test the limits of these approaches. They’d find edge problems (designing databases, remote teams, etc)…
Recently my friend Lars Hupel and I had a discussion on why formal methods don’t compose well. You can read the conversation here. We focused mostly on composing formally-verified code. I want to talk a little more about the difficulties in composing specifications. This is half because it’s difficult for interesting…
There’s not a whole lot on TLA+ technique out there: all the resources are either introductions or case studies. Good for people starting out, bad for people past that. I think we need to write more intermediate-level stuff, what Ben Kuhn calls Blub studies. Here’s an attempt at that. Most TLA+ properties are…