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California Police Can Start Ticketing Driverless Cars

https://www.nytimes.com/2026/04/30/us/california-ticket-driverless-car-violations.html
1•reaperducer•57s ago•0 comments

Show HN: Listen to Hacker News on the Go

https://hncast.com
1•ynarwal__•2m ago•0 comments

Show HN: BetterClaw – Compile a paragraph into a workflow that gates agent tools

1•infamous-oven•4m ago•0 comments

Supply Chain Security – Part 1

https://tinfoil.sh/blog/2026-05-01-supply-chain-client
1•3s•4m ago•0 comments

Warning over threat to birds after rat seen on Mousa

https://www.shetnews.co.uk/2026/04/30/warning-threat-birds-rat-seen/
1•latexr•5m ago•0 comments

A Deep Dive into Email Addresses

https://lasans.blog/articles/misc/email-addresses-deep-dive/
1•begoon•11m ago•0 comments

Fruit flies unexpectedly survived hypergravity and even reproduced

https://news.ucr.edu/articles/2026/04/30/under-crushing-hypergravity-flies-adapt-and-recover
1•giuliomagnifico•12m ago•0 comments

Show HN: "Woo", a multi-user world for agents

https://woo.hughpyle.workers.dev/
1•inguz•12m ago•0 comments

A new US phone network for Christians aims to block porn and gender-related con

https://www.technologyreview.com/2026/05/01/1136739/a-new-t-mobile-network-for-christians-aims-to...
1•joozio•19m ago•0 comments

Touch Typing Number Keys

https://susam.net/touch-typing-number-keys.html
1•susam•21m ago•0 comments

Apple accidentally left Claude.md files Apple Support app

https://xcancel.com/aaronp613/status/2049986504617820551
5•andruby•22m ago•0 comments

Your Website Is Not for You

https://websmith.studio/blog/your-website-is-not-for-you/
2•pumbaa•22m ago•0 comments

Show HN: Porting partially deobfuscated Old School Runescape to use LWJGL 3

https://github.com/stevefan1999-personal/void-client/tree/feat/native-to-java-port
1•stevefan1999•22m ago•0 comments

Turn Git commits and PRs into automated team updates (Slack/email)

https://gitmore.io
2•dmsozpepnc•23m ago•0 comments

The Network

https://www.citadel21.com/the-network
1•olalonde•23m ago•0 comments

New computer chip material inspired by the human brain could slash AI energy use

https://www.cam.ac.uk/research/news/new-computer-chip-material-inspired-by-the-human-brain-could-...
1•breve•24m ago•0 comments

Aaron Hsu: My favorite verbose programming technique [video]

https://www.youtube.com/watch?v=hkNwku81ehw
1•tosh•25m ago•0 comments

The Most Privacy-Respecting Search Engine

https://hister.org/posts/hister-the-most-privacy-respecting-search-engine
6•mstef•27m ago•0 comments

Company says nuclear fusion could power the grid – and soon

https://www.cnn.com/2026/04/30/climate/nuclear-fusion-real-world-electricity-grid
2•robtherobber•28m ago•0 comments

Parallel Pi coding agents in a sandbox

https://github.com/CelestoAI/SmolVM
2•theaniketmaurya•28m ago•3 comments

Show HN: Revdoku – visual document review with AI (open-source)

https://github.com/revdoku/revdoku
1•eummm•29m ago•0 comments

Notes on a non-profit indicted for bank fraud

https://www.bitsaboutmoney.com/archive/nonprofit-indicted-bank-fraud/
2•greyface-•29m ago•0 comments

Is this roadmap for back end realistic?

1•helloeveryone•30m ago•0 comments

Liar's Valuation

https://writing.nikunjk.com/p/liars-valuation
2•maxua•30m ago•0 comments

Show HN: Bitcoin Monitor Widget

https://btcwid.com
1•hda_ycombinator•38m ago•0 comments

TV Pickup

https://en.wikipedia.org/wiki/TV_pickup
3•piker•41m ago•0 comments

AI Mock Interviewer That Challenges You – LoopPass [video]

https://www.youtube.com/watch?v=a4oMH7spG8c
1•tomerbd•41m ago•0 comments

The AI Jailbreakers

https://www.theguardian.com/technology/2026/apr/29/meet-the-ai-jailbreakers-i-see-the-worst-thing...
1•saikatsg•47m ago•0 comments

Show HN: We Rebuilt AppAnne and Created Appkittie

https://www.appkittie.com
48•tadasg•49m ago•0 comments

Children Went from Worthless to Priceless (2013)

https://priceonomics.com/the-price-of-a-child/
1•downbad_•54m ago•1 comments
Open in hackernews

Understanding-j: An introduction to the J programming language that gets to the

https://github.com/bugsbugsbux/understanding-j
62•todsacerdoti•12mo ago

Comments

prezjordan•12mo ago
To the author: you can add a .devcontainer directory with a Dockerfile, allowing folks to try this in their browser with GitHub Codespaces

Shameless plug, feel free to copy my setup! https://github.com/jdan/try-j

userbinator•12mo ago
Unintentional humour with how the title got cut off?
pixelpoet•12mo ago
The title stops just short of the
johnisgood•12mo ago
"to the point", I presume, based on its README.
pjmlp•12mo ago
A side effect of the small length available for titles and the whole titles should not be editoralised point of view.
Jtsummers•12mo ago
It's more an issue of todsacerdoti not checking their submission titles will fit, they do this a lot with their submissions. Abbreviating titles is not frowned upon when they don't fit, I've never had any reverted to something like this submission's title because I (for instance) shortened "United States" to "US" to shave off 11 characters.

In this case, cutting out the superfluous "programming language" part would get you "Understanding-j: An introduction to J that gets to the point" which would fit just fine. When in doubt, include the original title in a comment to explain the edit and let the mods sort it out later.

detaro•12mo ago
It's hard to check if titles fit if you use a bot to repost from other sites.
Jtsummers•12mo ago
Fair, they're lazy and can't be bothered to fix their bot even after 5 years of submitting messed up titles.
t-writescode•12mo ago
From the doc,

  _3                  NB. negative numbers start with underscore
  _                   NB. sole underscore is infinity: a number
  __                  NB. negative infinity
Is this a standard I'm unaware of?
avmich•12mo ago
The use of underscore for negative numbers is J's choice, explained e.g. here - https://www.jsoftware.com/docs/help807/jforc/preliminaries.h... .

Explicitly representing infinity, and working with it in some cases, allows to reduce number of exceptions...

Avshalom•12mo ago
APL used ¯3 for negative 3; J went underscore to be similar but ascii.
gitroom•12mo ago
Underscore stuff always throws me off - never quite got used to how J does it. Gotta respect the weird choices though.
jbverschoor•12mo ago
Not the same as (Visual) J++. Great IDE btw
vintagedave•12mo ago
I’ve recently come to be fascinated by J.

Twenty years ago, studying my computing degree, one semester we learned J. It was unlike anything I’d used before and the entire class found it confusing. The compiler / environment was reportedly written by one of the professors and it was routine to run into bugs; I remember puzzling through something, going to a tutor, and them just shrugging it off as a J interpreter issue. I never grokked it and simply passed the course.

But it keeps on recurring to me and I pause to think of J at the weirdest times. As I use more and more languages, I’ve become more fascinated by it. Just like Prolog (also one semester, but with a reliable environment.) I want to learn both better.

binary132•12mo ago
I’ve been thinking for the past couple of years that the ideal programming language would be something like a combination of a concatenative language (a la FORTH) and an array programming language.
gnubison•12mo ago
Uiua?
binary132•12mo ago
interesting, I have not seen this one
preguntador•12mo ago
12j34 is 12j + 34 or 12 + 34j?
quartern•12mo ago
12 + 34j as per https://code.jsoftware.com/wiki/Vocabulary/Constants#Complex...