
Haskell jock. Backend Developer UX at @mercury. I wrote @prodhaskell so you can get a Haskell job!
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Joined February 2013
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Matt Parsons retweeted
I strongly believe there are entire companies right now under heavy AI psychosis and its impossible to have rational conversations about it with them. I can't name any specific people because they include personal friends I deeply respect, but I worry about how this plays out.
I lived through the great MTBF vs MTTR (mean-time-between-failure vs. mean-time-to-recovery) reckoning of infrastructure during the transition to cloud and cloud automation. All those arguments are rearing their ugly heads again but now its... the whole software development industry (maybe the whole world, really).
It's frightening, because the psychosis folks operate under an almost absolute "MTTR is all you need" mentality: "its fine to ship bugs because the agents will fix them so quickly and at a scale humans can't do!" We learned in infrastructure that MTTR is great but you can't yeet resilient systems entirely.
The main issue is I don't even know how to bring this up to people I know personally, because bringing this topic up leads to immediately dismissals like "no no, it has full test coverage" or "bug reports are going down" or something, which just don't paint the whole picture.
We already learned this lesson once in infrastructure: you can automate yourself into a very resilient catastrophe machine. Systems can appear healthy by local metrics while globally becoming incomprehensible. Bug reports can go down while latent risk explodes. Test coverage can rise while semantic understanding falls. Changes happens so fast that nobody notices the underlying architecture decaying.
I worry.
Production Haskell by Matt Parsons is on sale on Leanpub! Its suggested price is $40.00; get it for $22.50 with this coupon: leanpub.com/production-haske… @mattoflambda #haskell
Matt Parsons retweeted
No-one has figured out how an eng team should work with agents yet. Be wary of anyone telling you they know how to do it. Keep exploring. blog.exe.dev/bones-of-the-so…
Matt Parsons retweeted
Replying to @chrislakin
idk if this is familiar, but I have tracked when techniques fail/succeed, and when they do succeed they only succeed once.
Self-CBT fixed my depression for years once, but it never worked when it came back.
“Just one more day” worked for 3 months, but never again after 1 fail.
Matt Parsons retweeted
Friends, I'm opening a spiritual center in Boulder!
It's called Nameless Mountain, and it's focused on spiritual maturity rather than enlightenment.
We're trying to raise $50,000 to cover this year's expenses. Please help build this with us by donating or becoming a member:
givebutter.com/nameless-moun…
Matt Parsons retweeted
One of the cool thing about the AI revolution is that spending a lot of effort on error messages is cool again, because the agents actually read the error messages!
Matt Parsons retweeted
New blog post: "A sufficiently detailed spec is code"
I wrote this because I was tired of people claiming that the future of agentic coding is thoughtful specification work. As I show in the post, the reality devolves into slop pseudocode
haskellforall.com/2026/03/a-…
Matt Parsons retweeted
NixCI is getting a cool suite profile view that lets you see why your CI is as fast/slow as it is.
Matt Parsons retweeted
If you don’t have lambda and cannot articulate lambda why would I choose to invest. There are other teams which both can use modern tools and also have lambda.
(I have decided since no one popularized word yet: lambda is the general factor of performance above SOTA LLM baseline)
Matt Parsons retweeted
"Parse, don't validate" but in Rust instead of Haskell
harudagondi.space/blog/parse…
Matt Parsons retweeted
In the future, Haskell users will be able to annotate their programs to get better stack traces, thanks to work by the Well-Typed team: well-typed.com/blog/2025/09/…
Matt Parsons retweeted
Replying to @mattoflambda
9.10.2 ghci reloads got quite fast for me. 9.10.1 is super slow.
9.8.4 is also really fast. But < 9.8.4 is super slow.
@romesrf fixed a GHC bug that impacted the reload times.
Matt Parsons retweeted
Not really a response, but I like GADTs and wrote a small article with a nice example use-case. It's about an #eventsourcing API in a #haskell back-end. Link below (sigh) ⬇️
Matt Parsons retweeted

Andrej Karpathy@karpathy25 Dec 2024
United States
United StatesConnected via United States App StoreAccount-level information, not a live location or per-post device.
Nice post on software engineering.
"Cognitive load is what matters"
minds.md/zakirullin/cognitiv…
Probably the most true, least practiced viewpoint.
Matt Parsons retweeted
My latest article "Plucking constraints in Bluefin" explain Bluefin's use of the typeclass system to safely allow removing effects from scope:
h2.jaguarpaw.co.uk/posts/blu…
Matt Parsons retweeted
I'm giving a talk about Haskell at @mercury at the upcoming Silicon Valley Haskell Meetup. Come join if you're in the Bay Area
The next Silicon Valley Haskell Meetup is on Sep 6, 5:30pm, at @MatXComputing HQ in Mountain View.
We'll have @taktoa1 (MatX) talk about compiler design, and @GabriellaG439 (@mercury) talk about Haskell at Mercury.
RSVP here lu.ma/i70wtx3t
Matt Parsons retweeted
I wrote a blog post on how to document a database schema, based on my experience @mercury
mercury.com/blog/documenting…
Quality schema docs are a great investment for an engineering team—database tables are probably the core data structures of your app, and the docs enable data science and product to query the DB without help from Eng
Matt Parsons retweeted
Started reading @prodhaskell some weeks ago and so far I'm really enjoying it, maybe I will create a thread with the interesting things I've learned! #Haskell
Matt Parsons retweeted
Production Haskell by Matt Parsons is on sale on Leanpub! Its suggested price is $40.00; get it for $22.50 with this coupon: leanpub.com/sh/TDw4avef @mattoflambda #Haskell



























