Sjoerd Visscher

GHC has slow compile times because otherwise the #Haskell programmers would be far too productive. Balance must be maintained.

foldMap!

Something like this would be nice (especially if it would perform as well): foldMap \(Sigma tag val) -> Pi \tag’ -> if (tag == tag’) then [val] else []

The Clowder Project: An online resource for category theory and mathematics Logo is an associator pentagon with space cats.

From the "Progress" page: Eventually, they too grew too large for their format, as had happened before. Organizing them in PDF form kept getting more and more difficult. For instance, during its last year, compilation was taking 8 hours, and LuaLaTeX had to be recompiled specifically to increase certain built-in limits. Indeed, the last compiled PDF of the project ran at 10566 pages.

10,566 pages of category theory notes (that took 8 hours to compile) now in process of converting to Stacks Project format: www.clowderproject.com/index.html 🧮

It's always traverse, as per @clementd.wtf

Honestly, don't bother learning about par and pseq, parTraversable is the only thing you need. #haskell #parallelism

Pure parallelism, my favorite form of parallelism!

1. Researching this week’s column, I felt that I understood at last just why, on so many issues – benefits, Gaza, environmental and planning laws, anti-protest laws, bank deregulation, fiscal rules etc - Labour is out-Torying the Tories. Why it has become so cruel, so destructive and so spineless. 🧵

Sjoerd Visscher (@sjoerd_visscher@types.pl) Attached: 3 images I believe proarrow equipments are a great setting to study optics in. You can see the expression for optics and the equivalent string diagram below. The string diagram even looks like it's just a schematic drawing of an optic, but it really contains all the required information! The arrow heads indicate that s, t, a and b are all tight arrows, but in the loose direction. If you specialize to the proarrow equipment of functors and profunctors and simplify, you get the final expression. And if you then make S and T constant functors, and A and B monoidal actions, you get back mixed optics. #categorytheory #optics

I believe proarrow equipments are a great setting to study optics in! Read more in my mastodon post:
types.pl/@sjoerd_viss...

As a “senior man in tech”, I can only wholeheartedly support this article. The observations and conclusions very much match what I have seen and concur with the experiences I heard from other women. We (= the men) need to do better!

Sjoerd Visscher (@sjoerd_visscher@types.pl) Attached: 3 images I believe proarrow equipments are a great setting to study optics in. You can see the expression for optics and the equivalent string diagram below. The string diagram even looks like it's just a schematic drawing of an optic, but it really contains all the required information! The arrow heads indicate that s, t, a and b are all tight arrows, but in the loose direction. If you specialize to the proarrow equipment of functors and profunctors and simplify, you get the final expression. And if you then make S and T constant functors, and A and B monoidal actions, you get back mixed optics. #categorytheory #optics

I believe proarrow equipments are a great setting to study optics in! Read more in my mastodon post:
types.pl/@sjoerd_viss...

Who is doing the most exciting work at the intersection of PL and LLMs right now?

A simple formalization of alpha-equivalence While teaching untyped $λ$-calculus to undergraduate students, we were wondering why $α$-equivalence is not directly inductively defined. In this paper, we demonstrate that this is indeed feasible. Sp...

A simple formalization of alpha-equivalence. ~ Kalmer Apinis, Danel Ahman. arxiv.org/abs/2507.10181 #ITP #Rocq

How GHC is evolving to support WebAssembly and why it mattersCheng Shao presents the architecture, challenges, and current status of the GHC backend for WebA... Compiling Haskell to WebAssembly – Cheng Shao (GHC/Wasm Backend Developer)

The videos for Zurihac 2025 are online. Our own Cheng Shao, main author of GHC's Wasm backend, taught everything you need to know to build your own Haskell Wasm app in five lessons. www.youtube.com/watch?v=9zv0...

What about you? What was your favourite presentation?

Profunctor Laws dimap id id = id: OK 27 tests completed dimap composition: OK (62.03s) 14348907 tests completed

Smallcheck fun: Let's just check the (->) profunctor instance on functions on a tiny datatype, say data Three = A | B | C.

Hmm, why is it taking so long?? Oh, there are 27 functions of type Three -> Three, and the composition test takes 5 of those, that's 27^5 :-)

Having been subjected to Javascript for over 20 years, I still only got 16/28. This really is insane!

new Date("wtf") How well do you know JavaScript's Date class?

I scored 9/28 on jsdate.wtf and all I got was this lousy text to share on social media. This is insane @rich-harris.dev 🤯

Dank! Het heeft zijn voors en tegens zie ik nu.

De lopend 10-jaarsgemiddelde lijn is nog steeds behoorlijk grillig, zou een nog langer lopende gemiddelde lijn erbij interessant zijn?

Explosie in elektriciteitskast van NS-trein kwam door kapot onderdeel Het defecte onderdeel is volgens de spoorvervoerder een "specifiek type condensator in de installatie van de trein".

There's a (very recent) Xkcd for that!

nos.nl/artikel/2573...

xkcd.com/3106/

You should search for "mandelbrot effect", including quotes, on google right now (with AI turned on).

does anyone know, like, a LOT about nix, and would be willing to help me clean up nix build stuff for a huge project at work? it's OSS, and i could pay u :3

Really proud to live in the Netherlands seeing this list.

Wij hebben hier ook net onze wandeling erop zitten om dezelfde reden!

TIL Haskell's bitshift-right operator works on strings, too!

main = do
putStrLn ("22" >> "1")
putStrLn ("891" >> "2")

How is this different from `fromJust` being in base?

I.e. only separately functorial in each argument, they only allow the funny tensor product between categories.

Physicality: the new age of UI There’s a lot of rumors of a big impending UI redesign from Apple. Let’s imagine what’s (or what could be) next for the design of iPhones, Macs and iPads.

I wrote some words and made some renders on what the New Design Language of iOS, iPadOS and macOS might be. Physicality: The new age of UI. www.lux.camera/physicality-...

proarrow/src/Proarrow/Category/Instance/ZX.hs at main · sjoerdvisscher/proarrow Haskell library for doing category theory with a central role for profunctors - sjoerdvisscher/proarrow

You can hate on LLMs all you want, but with help from ChatGPT I was able to implement a bit of quantum computing, something I wouldn't have been able to do on my own. github.com/sjoerdvissch...

It warms up my hands.