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2× – nine months later: We did it (Intercom)

https://ideas.fin.ai/p/2x-nine-months-later
1•mmarian•1m ago•0 comments

This Slug Can Survive on Photosynthesis [video]

https://www.youtube.com/watch?v=IH_uv4h2xYM
1•CharlesW•1m ago•0 comments

KDE at 30

https://kde.org/anniversaries/30/
2•kristianp•3m ago•0 comments

Apple's Cal AI crackdown signals it's still policing the App Store

https://techcrunch.com/2026/04/21/apples-cal-ai-crackdown-signals-its-still-policing-the-app-store/
1•CharlesW•3m ago•0 comments

The Infamous Coin Toss

https://ergodicityeconomics.com/2023/07/28/the-infamous-coin-toss/
1•efavdb•4m ago•0 comments

Global growth in solar "the largest ever observed for any source"

https://arstechnica.com/science/2026/04/global-growth-in-solar-the-largest-ever-observed-for-any-...
2•tambourine_man•5m ago•0 comments

Google Gemini Deep Research Agents Now Search Both Web and Private Data via MCP

https://the-decoder.com/google-launches-deep-research-and-deep-research-max-agents-to-automate-co...
1•demiurges•7m ago•0 comments

Meta will record employees' keystrokes and use it to train its AI models

https://techcrunch.com/2026/04/21/meta-will-record-employees-keystrokes-and-use-it-to-train-its-a...
1•cebert•8m ago•1 comments

San Diego rents declined more than 19 of 20 top US markets after surge in supply

https://www.kpbs.org/news/economy/2026/03/27/san-diego-rents-declined-more-than-19-of-nations-top...
5•littlexsparkee•9m ago•0 comments

I'm Sick of AI Everything

2•jonthepirate•11m ago•0 comments

Show HN: Twitter Bookmarks Downloader – Export and Bulk Delete X Bookmarks

https://chromewebstore.google.com/detail/twitter-bookmarks-downloa/kgmbiokleeacfnkfihheldbdapoifclb
1•qwikhost•12m ago•0 comments

The Wild Story of the Teton Dam Failure

https://www.youtube.com/watch?v=J7ieKmP96Hc
1•mhb•14m ago•0 comments

NASA Moonbound Episode 1 [video]

https://www.youtube.com/watch?v=bfw4G59j9uw
1•BiraIgnacio•16m ago•0 comments

Kubuntu 26.04 Beta – Resolute Raccoon

https://kubuntu.org/news/kubuntu-26-04-beta/
1•kristianp•17m ago•0 comments

Google WeatherNext 2 – Our most accurate AI weather forecasting technology

https://deepmind.google/science/weathernext/
1•Anon84•19m ago•0 comments

Topologies on Finite Groups that Contain Proper Subgroups

https://m-slee.netlify.app/posts/finite-topo-subgroups
1•richard_chase•20m ago•0 comments

Show HN: PayClaw – Give your AI agent a wallet it can spend

https://www.payclaw.me/
1•onsari•21m ago•0 comments

The Problem with Solutions (2024)

https://webdev.rip/notes/the-problem-with-solutions
2•mooreds•22m ago•1 comments

Florida AG launches criminal investigation into ChatGPT over FSU shooting

https://www.npr.org/2026/04/21/nx-s1-5793967/florida-openai-investigation-mass-shooting-fsu
1•pseudolus•24m ago•0 comments

Building a Platform Is a Balancing Act

https://matthewboston.com/blog/building-a-platform-is-a-balancing-act.html
2•bostonaholic•30m ago•0 comments

Rich Sutton's University of Alberta Convocation Address

http://www.incompleteideas.net/IncIdeas/ConvocationAddress.html
3•mercurybee•33m ago•0 comments

Show HN: Group Relative Policy Optimization, visualized step by step

https://adamsohn.com/grpo/
1•dataviz1000•35m ago•0 comments

OpenAI Under Criminal Probe in Florida over Mass Shooter's ChatGPT Use

https://www.wsj.com/us-news/law/openai-under-criminal-probe-in-florida-over-mass-shooters-chatgpt...
2•reed1234•41m ago•1 comments

New Drugs for Pancreatic Cancer Show Remarkable Promise for Deadly Disease

https://www.wsj.com/health/healthcare/new-drugs-for-pancreatic-cancer-show-remarkable-promise-for...
3•megacorp•43m ago•0 comments

We translated the Palantir manifesto for actual human beings

https://www.theverge.com/policy/915237/palantir-manifesto
3•tastyface•44m ago•1 comments

Voxyflow – An AI companion that plans, codes, and ships with you

https://github.com/jcviau81/voxyflow
1•jcviau•44m ago•0 comments

A true story about interviewing at Google in 2006

https://www.threads.com/@peternbiddle/post/DXaCcKuEvAA
4•Anechoic•45m ago•2 comments

Anthropic tests how devs react to yanking Claude Code from Pro plan

https://www.theregister.com/2026/04/22/anthropic_removes_claude_code_pro/
1•angrydev•46m ago•2 comments

Revisit Your Old Ideas

https://www.robot-future.com/preview/69e8117520bc1661002087bc
1•robot-future•47m ago•0 comments

Weaponized Deepfakes

https://www.technologyreview.com/2026/04/21/1135652/weaponized-deepfakes-ai-artificial-intelligence/
1•gnabgib•48m ago•0 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•11mo ago

Comments

prezjordan•11mo 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•11mo ago
Unintentional humour with how the title got cut off?
pixelpoet•11mo ago
The title stops just short of the
johnisgood•11mo ago
"to the point", I presume, based on its README.
pjmlp•11mo ago
A side effect of the small length available for titles and the whole titles should not be editoralised point of view.
Jtsummers•11mo 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•11mo ago
It's hard to check if titles fit if you use a bot to repost from other sites.
Jtsummers•11mo 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•11mo 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•11mo 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•11mo ago
APL used ¯3 for negative 3; J went underscore to be similar but ascii.
gitroom•11mo ago
Underscore stuff always throws me off - never quite got used to how J does it. Gotta respect the weird choices though.
jbverschoor•11mo ago
Not the same as (Visual) J++. Great IDE btw
vintagedave•11mo 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•11mo 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•11mo ago
Uiua?
binary132•11mo ago
interesting, I have not seen this one
preguntador•11mo ago
12j34 is 12j + 34 or 12 + 34j?
quartern•11mo ago
12 + 34j as per https://code.jsoftware.com/wiki/Vocabulary/Constants#Complex...