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How should we think about error-handling in concurrent programs? In single-threaded programs, we’ve mostly converged on a standard pattern, with a diverse zoo of implementations and concrete patterns. When an error occurs, it is propagated up the stack until we find a stack frame which is prepared to handle it. As we do so, we unwind the stack frames in-order, giving each frame the opportunity to clean up or destroy resources as appropriate.
For a while now, I’ve been fascinated by Z3 and by SMT solving more broadly. While on pat leave recently, I was reminded of the existence of regular-expression crossword puzzles, and allowed myself to get nerdsniped by writing a Z3-backed solver. I expected to spend perhaps an afternoon cranking out a quick solver; I ended up getting sucked into understanding and debugging Z3 performance, and learning far more about Z3 and about SMT than I expected.
While investigating the performance of the new Python 3.14 tail-calling interpreter, I learned (via this very informative comment from Sam Gross) new (to me) piece of performance trivia: Modern CPUs mostly no longer struggle to predict the bytecode-dispatch indirect jump inside a “conventional” bytecode interpreter loop. In steady-state, assuming the bytecode itself is reasonable stable, modern CPUs achieve very high accuracy predicting the dispatch, even for “vanilla” while / switch-style interpreter loops1!
About a month ago, the CPython project merged a new implementation strategy for their bytecode interpreter. The initial headline results were very impressive, showing a 10-15% performance improvement on average across a wide range of benchmarks across a variety of platforms. Unfortunately, as I will document in this post, these impressive performance gains turned out to be primarily due to inadvertently working around a regression in LLVM 19. When benchmarked against a better baseline (such GCC, clang-18, or LLVM 19 with certain tuning flags), the performance gain drops to 1-5% or so depending on the exact setup.
Earlier this month, I used Claude to port (parts of) an Emacs package into Rust, shrinking the execution time by a factor of 1000 or more (in one concrete case: from 90s to about 15ms). This is a variety of yak-shave that I do somewhat routinely, both professionally and in service of my personal computing environment. However, this time, Claude was able to execute substantially the entire project under my supervision without me writing almost-any lines of code, speeding up the project substantially compared to doing it by hand.
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Associate Professor Cathy Wu uses reinforcement learning to help map out improvements to transportation and other multifaceted systems.
After living with Apple’s 27.0 OSs since launch, I have some more annoyances to get off my chest. This time, it’s all about how tabs and menus have gotten worse. I’ve already ranted about the Liquid Glass material in general, but these two design changes in particular have really been grinding my gears. I’ll reiterate that Apple’s latest OSs look substantially nicer to me than the previous set… but that only makes these setbacks more glaring. Also, many of these issues aren’t nearly as bad in light mode — but I use dark mode exclusively on all platforms. Apple offers this appearance setting, so I think it’s fair to criticize them when it’s not holding up. First up, let’s talk tab bars. I think these looked awful in the original Liquid Glass redesign, and in 27.0 they look even worse. Below is an example of three tab bars from Safari in macOS. All of them are in dark mode. The top example is from macOS 26 with the “clear” Liquid Glass setting, the middle is macOS 27 with the default (mid-slider) version of Liquid Glass, and the bottom is macOS 27 with Liquid Glass at its most tinted. In each, the middle tab is selected (though I think the word “tab” is being quite generous to these globs). In macOS 26, there was practically no difference between the clear and tinted versions of tabs. Similarly, the clearest and default/middle tabs in macOS 27 are effectively the same. Because of this, I’m leaving out the redundant examples. Even though I still think it’s ugly, I vastly prefer the macOS 26 version of these three options. It offers the most contrast, and it makes more sense in dark mode: the background is darker and the foreground of the active tab is lighter. The middle example is what tabs look like in the default (mid-slider) version of Liquid Glass in macOS 27. There’s now only a very faint outline around the active tab, and practically no difference in background colours. To me, this is unreasonably subtle. The effect is even worse when there are a lot of tabs open. Lastly, there’s macOS 27 with the fully tinted Liquid Glass setting. It’s better, but it still looks less correct to me than the tab design from macOS 26. It’s difficult to put into words how much I loathe the look of this new tab bar design. I don’t mind the more “bubbly” look of Liquid Glass throughout the 27 OSs for the most part. It gives UI elements more dimension than in the 26 OSs. But it doesn’t work for tabs. Because the bubbly look is inside a trough, the active tab’s glass effect ends up looking like a blur on the top and bottom. This reduces contrast further and makes the active tab harder for me to pick out. Even in dark mode with full tint, I find the active tab less visually clear than in 26’s clear mode. Now, I’m sure there are at least a few people reading who don’t see what the fuss is about. If that’s you, I assure you that the difference is more stark when you’re not comparing things side by side. It’s not impossible for me to pick out the active tab, but I think it’s trickier than it needs to be! But, if you still don’t believe me, here’s a little experiment. Which of these do you think is most legible? The text/background colours in the above image are based on the foreground/background colours used in the tab bar instances above. First is clear in macOS 26, then the default from macOS 27, then fully tinted in macOS 27. I think they’re all pretty awful, but I prefer the macOS 26 clear version. Again, this is because I’m using dark mode. In dark mode, light text appears on a darker background. Similarly, active UI elements have a lighter background than their surrounding elements. I’m sure there are counter-examples, but this is how just about everything else works in Apple’s own apps! It should be noted that Safari uses the system default tab bar design. I also see this design in Apple’s Terminal app, in Pixelmator Pro, and elsewhere. I don’t use Xcode daily anymore, but you’ll also find them there — though in true Xcode fashion, they’re ever so slightly nonstandard and also don’t respect your tint setting. Below is a screenshot of Xcode using my current settings of dark mode with fully tinted Liquid Glass. Up next: menus. Below is an image showing four versions of the same menu in macOS. Top left is macOS 26 clear, top right is macOS 26 tinted, bottom left is macOS 27 default (mid-slider), and bottom right is macOS 27 fully tinted. It’s a similar story here. In macOS 26’s dark mode, I had no problem with system menus even when Liquid Glass was set to clear. In macOS 27, even in the fully tinted mode, the menus have much lower contrast. They also now lose all of Liquid Glass’s refractive effects when at their most tinted. I think this is less of an issue than the tab design changes, but it’s still a downgrade. Again, I’m certain many people don’t care about this. Some might wonder why I’m not turning on accessibility settings to help with these things, if they bother me so much. I’ve flirted with this (especially the “Increase Contrast” setting), but those settings have many knock-on effects. 1 But honestly, I don’t think accessibility settings should be required to have a reasonable amount of contrast in a design system. Maybe Apple disagrees, but I really hope more dark mode tweaks are coming. The “Increase Contrast” setting is under System Settings -> Accessibility -> Display -> Increase Contrast. Interestingly, you can use this setting along with the clearest version of Liquid Glass to almost get back to how things looked in macOS 26’s version of tinted. However, it adds contrast-y lines around many UI elements that I find extremely distracting. It also alters colours on some elements to, strangely, make them less contrast-y. It feels unevenly applied and poorly implemented in several apps. ↩
Trump wants to add a citizenship question and ban questions on race
I recently watched the talk by Scott Jenson titled "Are we really going to use the same Desktop UX forever?" https://www.youtube.com/watch?v=V7AfAcQwLW0&t=445s. He's a great presenter, really articulate and concise. The kind of speaker that you'd
