Hacker News: leprechaun1066

New comment by leprechaun1066 in "Programming in K"

leprechaun1066 — Mon, 02 Mar 2026 00:07:19 +0000

The aj function at its heart is a bin (https://code.kx.com/q/ref/bin/) search between the two tables, on the requested columns, to find the indices of the right table to zip onto the left table.

  aj[`sym`time;t;q]

becomes

  t,'(`sym`time _q)(`sym`time#q)bin`sym`time#t

The rest of the aj function internals are there to handle edge cases, handling missing columns and options for filling nulls.

A lot of the joins can be distilled to the core operators/functions in a similar manner. For example the plus-join is

  x+0i^y(cols key y)#x

New comment by leprechaun1066 in "Claws are now a new layer on top of LLM agents"

leprechaun1066 — Sat, 21 Feb 2026 14:00:00 +0000

> just like LLM agents were a new layer on top of LLMs, Claws are now a new layer on top of LLM agents, taking the orchestration, scheduling, context, tool calls and a kind of persistence to a next level.

Layers of "I have no idea what the machine is doing" on top of other layers of "I have no idea what the machine is doing". This will end well...

New comment by leprechaun1066 in "I ported JustHTML from Python to JavaScript with Codex CLI and GPT-5.2 in hours"

leprechaun1066 — Wed, 17 Dec 2025 01:33:39 +0000

In this case the majority of the work was done by another company on your instruction. When you signed up was there anything in the terms that said you get ownership over the output?

New comment by leprechaun1066 in "Waymo is bringing autonomous, driverless ride-hailing to London in 2026"

leprechaun1066 — Thu, 16 Oct 2025 10:13:36 +0000

Wayve have been working on London streets for some time now. This is from a few months ago:

https://www.youtube.com/watch?v=KvctCbVEvwQ

New comment by leprechaun1066 in "GPT-5o-mini hallucinates medical residency applicant grades"

leprechaun1066 — Tue, 14 Oct 2025 15:38:14 +0000

Another way to look at it is everything a LLM creates is a 'hallucination', some of these 'hallucinations' are more useful than others.

I do agree with the parent post. Calling them hallucinations is not an accurate way of describing what is happening and using such terms to personify these machines is a mistake.

This isn't to say the outputs aren't useful, we see that they can be very useful...when used well.

New comment by leprechaun1066 in "SQL Injection as a Feature"

leprechaun1066 — Wed, 23 Jul 2025 12:57:33 +0000

Most applications backed kdb+ do just this. It comes with its own parser and you can query tables using something like an ast.

For example the user might ask for data with the constraint

  where TradingDesk=`Eq, AvgPx>500.0

which kdb+ parses into

  ((=;`TradingDesk;(),`Eq);(>;`AvgPx;500.0))

As a dev on the system I can then have a function which takes in this constraint and a list of clients that I want to restrict the result to. That list of clients could come from another function related to the entitlements of the user who made the request:

  applyClientRestriction:{[constraint;clients] constraint,enlist(in;`Client;enlist clients)}

Which results in an extension of the constraint like this for two clients A and B:

  q)applyClientRestriction[((=;`TradingDesk;(),`Eq);(>;`AvgPx;500.0));`ClientA`ClientB]
  ((=;`TradingDesk;enlist`Eq);(>;`AvgPx;500.0);(in;`Client;enlist`ClientA`ClientB))

Then that gets passed to the function which executes the query on the table (kdb+ supports querying tables in a functional manner as well as with a structured query language) and the result has the restrictions applied.

It's really nice because, once parsed, it's list processing like in a lisp and not string processing which is a pain.

New comment by leprechaun1066 in "KX Community Edition"

leprechaun1066 — Wed, 16 Jul 2025 21:16:36 +0000

Given Wes McKinney created Pandas for quantitative analysis, it's possible that Pandas wouldn't exist if AQR were paying for a q license.

New comment by leprechaun1066 in "KX Community Edition"

leprechaun1066 — Wed, 16 Jul 2025 18:33:01 +0000

The overview here is better than the marketing:

https://code.kx.com/q4m3/0_Overview/

New comment by leprechaun1066 in "Why LLMs Can't Write Q/Kdb+: Writing Code Right-to-Left"

leprechaun1066 — Sun, 13 Jul 2025 18:40:17 +0000

That does require someone to know that the take operator continues to treat the y list as circular when x is a list.

I think this form might be a bit easier: {(x,x)#(x*x)#1,x#0}

New comment by leprechaun1066 in "Why LLMs Can't Write Q/Kdb+: Writing Code Right-to-Left"

leprechaun1066 — Wed, 09 Jul 2025 14:59:01 +0000

It's not because of the left of right evaluation. If the difference was that simple, most humans, let alone LLMs, wouldn't struggle with picking up q when they come from the common languages.

Usually when someone solves problems with q, they don't use the way one would for Python/Java/C/C++/C#/etc.

This is probably a poor example, if I asked someone to write a function to create an nxn identity matrix for a given number the non-q solution would probably involve some kind of nested loop that checks if i==j and assigns 1, otherwise assigns 0.

In q you'd still check equivalence, but instead of looping, you generate a list of numbers as long as the given dimension and then compare each item of the list to itself:

  {x=/:x:til x}3

An LLM that's been so heavily trained on an imperative style will likely struggle to solve similar (and often more complex) problems in a standard q manner.

New comment by leprechaun1066 in "I struggled with Git, so I'm making a game to spare others the pain"

leprechaun1066 — Mon, 03 Mar 2025 13:57:15 +0000

I use perforce for my personal projects. Helix P4V's various ways of visualising streams, diffs and revisions are so nice.

New comment by leprechaun1066 in "Sid Meier's Civilization VII"

leprechaun1066 — Tue, 11 Feb 2025 11:02:36 +0000

These days it's usually better to try and find players on youtube or twitch than to read text based reviews.

New comment by leprechaun1066 in "Where is London's most central sheep?"

leprechaun1066 — Thu, 23 Jan 2025 11:30:32 +0000

> they're goats, as any self-respecting three year old could tell you

Sheep or goat? https://www.youtube.com/watch?v=dCzZN--4Its

New comment by leprechaun1066 in "Should you ditch Spark for DuckDB or Polars?"

leprechaun1066 — Mon, 16 Dec 2024 00:15:00 +0000

Financial market data (especially FX data) can have thousands of ticks per second. It's not unheard of for data engineers in that space to sometimes handle 1TB per day.

New comment by leprechaun1066 in "Elixir/Erlang Hot Swapping Code (2016)"

leprechaun1066 — Fri, 13 Dec 2024 11:00:16 +0000

We do this in q/kdb+ systems often for patches. An important thing about these languages is that this kind of workflow is part of the core for solving problems. So when you are building a system one of the aspects of its design will always allow for this update method. Then when you push a patch you both know the impact of the change (because you've tested the exact same steps in a dev/QA/UAT/Beta environment) and the work required to do it safely.

Major releases do go through a full shutdown and release cycle though.

New comment by leprechaun1066 in "AI hallucinations: Why LLMs make things up (and how to fix it)"

leprechaun1066 — Thu, 05 Dec 2024 00:40:29 +0000

Calling them hallucinations was a huge mistake.

New comment by leprechaun1066 in "Who died and left the US $7B?"

leprechaun1066 — Wed, 09 Oct 2024 01:57:27 +0000

In 2021/2022 there were 60 people in the UK who probably fall into that last group. Together their taxes accounted for about 1.4% of the UK tax bill despite being something like 0.002% of the population.

New comment by leprechaun1066 in "The Liberating Experience of Common Lisp"

leprechaun1066 — Tue, 01 Oct 2024 16:13:51 +0000

Shinmera recently talked about porting SBCL to the switch: https://reader.tymoon.eu/article/437

New comment by leprechaun1066 in "German Navy blasts out Darth Vader theme on Thames"

leprechaun1066 — Thu, 22 Aug 2024 13:20:49 +0000

A couple of old fogies down in Tunbridge Wells, "I say old chap, how very uncouth." Meanwhile everyone else, "It's been almost 50 years since Fawlty Towers. Took them long enough."

New comment by leprechaun1066 in "Awesome Engineering Games"

leprechaun1066 — Sun, 19 Nov 2023 22:02:50 +0000

Transport Fever 2 if you like choo-choos.