Tessera

Folgen

Alexis King

@lexi-lambda.bsky.social

computers can be understood • she/her, ⚢ • Chicago

70 Posts1663 Follower 8 Folgt

Alexis King @lexi-lambda.bsky.social · last wk.

The recording of my talk from Software Should Work is now up. :) www.youtube.com/watch?v=0BXu...

The Unreasonable Effectiveness of Constructive Data Modeling - Alexis King | SSW 2026

YouTube video by Software Should Work

youtube.com

Impure Pics @impurepics.bsky.social · last mo.

@lexi-lambda.bsky.social talks Racket, nonogram/picross puzzles, puzzle solvers, a functional picture combinator library on top of OpenGL, and programming for fun. Enjoy. youtu.be/LwpnwQGNC9Q

Having fun with Racket Nonograms (w/ Alexis King)

YouTube video by Impure Pics

youtu.be

Alexis King @lexi-lambda.bsky.social · 2mo ago

I am pleased to announce that I will be presenting at Software Should Work next month. I hope to see some of you there! :) softwareshould.work

Software Should Work

An independent conference on software reliability in Columbia, MO on July 16-17, 2026

softwareshould.work

Alexis King @lexi-lambda.bsky.social · 4mo ago

racket-nonogram can now show you any mistakes you’ve made, in case you can’t figure out what the issue was and don’t want to have to completely start over

Alexis King @lexi-lambda.bsky.social · 5mo ago

racket-nonogram now supports automatically generating “mega nonogram” puzzles from standard puzzles

Alexis King @lexi-lambda.bsky.social · 5mo ago

while working on this I have begun to understand why there are no mega picross implementations on the internet

;; fill-forced-tiles-in-mega-span!
;; : mega-tiles/c mega-placement-bound? mega-placement-bound?
;; #:set-full! (-> mega-index? any)
;; -> (values natural? line-affinity? line-affinity?)
;;
;; Given two mega placement bounds, fills any tiles forced by crosses along the
;; path bridging the two bounds. For example, suppose we have the following row:
;; ☒☐☐☐☐☐☐☒☐■
;; ■☐☐☒☐☐☐☐☐☐
;; This function will fill any tiles that must be filled to connect the two
;; filled boxes:
;; ☒☐■■■☐☐☒☐■
;; ■■☐☒☐☐■■■☐
;;
;; Along the way, it also calculates and returns the minimum number of tiles
;; that must be filled within the span, taking existing filled tiles into
;; account. It also returns two line affinities that can be used to calculate
;; the minimum cost of extending a placement with the given bounds backwards or
;; forwards, respectively. For example, given the row
;; ☐☐■☐☒☐☐☐
;; ☐☐☐☐☐■☐☐
;; then the results of this function applied with bounds (mega-placement-bound 0 2)
;; and (mega-placement-bound 1 5) will be as follows:
;;
;; 1. The returned minimum size will be 5, as at least 5 tiles must be filled
;; to bridge the two bounds.
;;
;; 2. The first line affinity will be #f, as one possible way to bridge the
;; two bounds is
;; ☐☐■☐☒☐☐☐
;; ☐☐■■■■☐☐
;; which fills both tiles in the first column. Therefore, it is possible to
;; extend the filled region backwards to either line at equal cost.
;;
;; 3. The second line affinity will be 1, as filling the tile in the first
;; line above the end bound would require filling 6 tiles, not five.
;; Therefore, extending the filled region forwards is biased towards the
;; second line.
;;
;; Note that the way this function interprets bounds with line 'both or 'either
;; can be somewhat counterintuitive; see Note [Filling forced tiles between
;; placement bounds] for an explanation.

This function is used in two different ways:

1. It is used to bridge the first and last filled tiles in a mega clue.
When used in this way, the bounds always refer to a specific line,
never 'both or 'either. This is the mode in which the return values
are utilized.

2. It is used to fill tiles forced by the intersection of the earliest
and latest tightest placements for a clue (or the intersection of one
such placement and a filled-in tile). This mode is called purely for
its side effects.

The interpretation of bounds supplied in the second case can be somewhat
counterintuitive, as they represent the greatest lower bound and least
upper bound for a clue’s placement, not tiles that must necessarily be
filled by the placement. For example, suppose we have the following empty
row for a mega 6 clue:
☐☐☐☐
☐☐☐☐
When we calculate the earliest and latest placements for this clue, we will
get the following two results:
▧▧▧☐ ☐▧▧▧
▧▧▧☐ ☐▧▧▧
The earliest placement has an end bound of (mega-placement-bound 'both 2)
and the latest placement has a start bound of (mega-placement-bound 'both 1).
The intersection of these bounds yields the following span:
☐▧▧☐
☐▧▧☐
This function will be called to fill any tiles forced within that span.
Given the fact that the bounds specify 'both lines, it would be easy to
mistakenly believe that all four tiles should be filled. However, that
would be completely wrong in this case, as the bounds do not specify which
tiles are (or should be) filled, they simply define the region inside which
forced tiles *may* be filled. In this example, there are no forced tiles,
so the proper behavior is to do nothing at all.

A natural followup question is to ask what the difference is between a
bound using 'both and a bound using 'either, or indeed what the difference
is between such a bound and one using a specific line. The answer lies in
what we consider to be “forced” at the span endpoints.

;; Note [Forced mega span endpoints]
;; ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
;; Endpoints of the span must be handled specially. Normally, we fill tiles
;; in one of the following shapes:
;; ■■■ ☐☒☐
;; ☐☒☐ ■■■
;; This corresponds to the span having to snake around a cross. However, at
;; consider the following row:
;; ☒☐☒☐☐☐☒
;; ☒☐☐☐☒☐☒
;; Suppose the span starts at the top left empty tile and ends at the bottom
;; right empty tile. If we only fill tiles in the above patterns, we’ll end up
;; with the following:
;; ☒☐☒■■■☒
;; ☒■■■☒☐☒
;; But this is missing the tiles at the ends! However, we don’t want to fill
;; the bounds unconditionally. Suppose instead we have the following row:
;; ☐☐☒☐☐☐☐
;; ☐☐☐☐☒☐☐
;; If the start and end locations are still the same, the tiles at the ends
;; are no longer forced. On the other hand, if we have the row
;; ☐☐☒☐☐☐☒
;; ☒☐☐☐☒☐☐
;; they *are* forced. Programmatically, the necessary conditions are:
;;
;; 1. The bound must cover 'both lines.
;; 2. The opposite tile must be bounded behind or afront.
;;
;; Somewhat counterintuitively, the second condition is all that matters, and
;; it holds regardless of whether the bound is the start bound or the end
;; bound. To illustrate, consider the following examples:
;; ☐☐▧☐☐ ☐☐▧☐☐
;; ☐☒☐☐☐ ☐☐☐☒☐
;; In both examples, ▧ represents a tile in one of the bound columns.
;; Regardless of whether we are filling from the left or the right, if the
;; bound’s line is 'both, the ▧ tile must be filled.

;; It is time to try to fill in boxes using the usual left/right
;; solve strategy. However, for mega clues, this is substantially
;; more complicated. We have to consider two cases separately:
;;
;; 1. If the earliest/latest placement overlaps with an existing
;; filled-in tile, we want to “extend” the filled region to the
;; placement’s bound. For example, suppose we have a mega 5
;; clue in the following row:
;; ☒☒☒☐☐
;; ☐■☐☐☐
;; Since the earliest placement’s end bound is larger than the
;; filled tile, we want to fill any tiles forced by crosses
;; from the tile to the bound:
;; ☒☒☒☐☐
;; ☐■■■☐
;;
;; 2. If the earliest/latest bounds overlap, we want to fill any
;; tiles forced by crosses between them. For example, suppose we
;; have a mega 5 clue in the following row:
;; ☒☐☐☐☐ ⇒ ☒■■■☐
;; ☐☐☒☒☐ ⇒ ☐☐☒☒☐
;;
;; It might seem as though tiles filled by the second rule would
;; always include those filled by the first, as long as we’ve placed
;; crosses appropriately to limit the size of the hole. Unfortunately,
;; this is not always true, at least with our current algorithm for
;; selecting an earliest/latest placement. For example, suppose we
;; modify the first example slightly:
;; ☒☒☐☐☐
;; ☐■☐☐☐
;; Here, there is no overlap guaranteed by the bounds alone, so if
;; we didn’t have any filled-in tiles, we wouldn’t be able to gain
;; any information.

Alexis King @lexi-lambda.bsky.social · 5mo ago

racket-nonogram now supports networked co-op multiplayer (and has a README) github.com/lexi-lambda/...

Alexis King @lexi-lambda.bsky.social · 5mo ago

it also supports mega picross-style puzzles now (I have not seen any other implementation of this in existence outside of the switch picross games)

Alexis King@lexi-lambda.bsky.social · 5mo ago

working on a nonograms implementation in racket based on the switch picross games github.com/lexi-lambda/...

Alexis King @lexi-lambda.bsky.social · 5mo ago

wrote a few paragraphs today about why early Stack Overflow was such a special and rewarding community to contribute to and why so many of us who were there have never really stopped mourning its slow but steady decay meta.stackoverflow.com/a/438314/465...

Tell me about the good old days, papa

I like this site. As both a scientist and an educator, it has allowed me to do the two things I love the most: continue learning, and teach where I can. I joined Stack Overflow late and didn't really

meta.stackoverflow.com

Alexis King @lexi-lambda.bsky.social · 5mo ago

working on a nonograms implementation in racket based on the switch picross games github.com/lexi-lambda/...

Alexis King @lexi-lambda.bsky.social · 6mo ago

mflatt: let’s ditch s-exps to make our language more accessible :) also mflatt: rhombus defines eight different ways an identifier can have a binding in the core language and the standard library adds several more. here is the documentation for how to define a basic datatype. do you like this

BNF from https://docs.racket-lang.org/rhombus-reference/class.html#%28def._%28%28submod._%28lib._rhombus%2Fprivate%2Famalgam..rkt%29._core%29._class._rhombus%2Fdefn%29%29

Body text from https://docs.racket-lang.org/rhombus-reference/class.html#%28def._%28%28submod._%28lib._rhombus%2Fprivate%2Famalgam..rkt%29._core%29._class._rhombus%2Fdefn%29%29

Alexis King @lexi-lambda.bsky.social · 6mo ago

really cool that stackoverflow-the-company is making such terrible choices that it’s gotten a wine mom with a radio and film degree to start fedposting in their moderator-only chatroom

Alexis King @lexi-lambda.bsky.social · 6mo ago

who else up experiencing some sort of "new-year" mind vacancy

Screenshot from langdev stack exchange chat that reads: “DannyNiu: Hi all, apologies for 2 poorly-received Q in a row. I'm experiencing some sort of "new-year" mind vacancy, and couldn't think straight.”

Alexis King @lexi-lambda.bsky.social · 8mo ago

it turns out to be a pretty big problem for internet “communities” how many people absolutely love feeling righteous anger and like to find as many opportunities as possible to be as mean and uncharitable as they want without feeling guilty

RJMacReady@rjmacready1529.bsky.social · 8mo ago

How can so many people read this as "i hate immigrants" and not "we dont have enough housing, the large amount of immigrants coming into the US were most vulnerable to this fact"

Alexis King @lexi-lambda.bsky.social · last yr.

love this completely insane guy who makes incredibly thorough, four hour long strategy videos for twenty year old mario party games for no discernible reason www.youtube.com/watch?v=Sndv...

Identifying Luck: Mario Party DS

YouTube video by ZoomZike

youtube.com

Alexis King @lexi-lambda.bsky.social · last yr.

jesus christ

Threads of tweets by @Ngnghm.

Lexi also complains about lack of female Haskellers. But Haskell recruits at the higher end of the IQ spectrum, and especially the math part of it. Between extra variance and skew towards shape rotators vs wordcels, males vastly dominate this population.

Extra variance means that males dominate both ends of the Bell curve for a lot of traits, from intelligent vs stupid to heroes vs criminals.

Unsurprisingly, a lot of the few women we find in these circles have obviously been exposed to a lot of testosterone during their development.

The human sexual dimorphism in cognitive abilities, behavior and preferences is obvious and ubiquitous despite the egalitarian religion destroying the West currently making its mention taboo.

Expecting equality or making it a goal is absurd, self-defeating, and, frankly, evil.

Instead, outliers should enjoy their status as such.

“One good Husband is worth two good Wives; for the scarcer things are, the more they're valued.” — Benjamin Franklin

Moreover, as a programmer, you're already an outlier in abilities and interests. And if you read this post, you're an outlier among these outliers. If you're female, even more so.

Alexis King @lexi-lambda.bsky.social · last yr.

I have published my first new blog post in four years lexi-lambda.github.io/blog/2025/05...

A break from programming languages

lexi-lambda.github.io

Alexis King @lexi-lambda.bsky.social · last yr.

DFB7-2278 is a SNES Game Genie code to make it so that enemy HP always shows up in Chrono Trigger regardless of whether you have the Sight Scope equipped. just in case anyone was wondering

Alexis King @lexi-lambda.bsky.social · last yr.

just wrote 2,300 words about register allocation langdev.stackexchange.com/a/4326/861

How do modern compilers choose which variables to put in registers?

C has the register keyword, originally designed as a hint to the compiler that a variable should be placed in a register rather than on the stack. However this is generally considered an unneeded f...

langdev.stackexchange.com

Alexis King @lexi-lambda.bsky.social · 2y ago

I’ve been thinking about this a lot lately, and I would add something: we must believe in something good. We must allow ourselves to believe that there are things in the world that are good and beautiful and true, and that they are worth defending and fighting for, without compromise.

Post nicht verfügbar.

Alexis King @lexi-lambda.bsky.social · 2y ago

update: someone has posted a remarkably extensive answer to this english.stackexchange.com/a/628758/17950

Origin of usage of “grovel” to mean rummage or exhaustively search

In computing circles, it is common to use the verb grovel to essentially mean to rummage or to exhaustively search. This usage is listed in The Jargon File, though no explanation as to its origin is

english.stackexchange.com

Alexis King@lexi-lambda.bsky.social · 2y ago

does anyone know the origin of the variant usage of “grovel” to mean “to rummage” or “to exhaustively search” commonly used in computing circles? if so, please answer my question on English Stack Exchange about this! english.stackexchange.com/q/628648/17950

Alexis King @lexi-lambda.bsky.social · 2y ago

@briangoetz.bsky.social would be lovely if you could write an answer to this question on langdev :) langdev.stackexchange.com/q/4265/861

Strings and arrays in Project Valhalla

My understanding of Project Valhalla's impact on arrays and Strings (please let me know if this is off): arrays will still be reference objects but an array of value objects may be flattened on th...

langdev.stackexchange.com

Alexis King @lexi-lambda.bsky.social · 2y ago

Origin of usage of “grovel” to mean rummage or exhaustively search

In computing circles, it is common to use the verb grovel to essentially mean to rummage or to exhaustively search. This usage is listed in The Jargon File, though no explanation as to its origin is

english.stackexchange.com

Alexis King @lexi-lambda.bsky.social · 2y ago

wrote an extremely lengthy answer to an interesting question about typechecking matching on polymorphic variants in a language with a sufficiently global type inference scheme, which I think illustrates just how challenging even “simple” things can easily become langdev.stackexchange.com/a/4250/861

Flow-sensitive type refinement of polymorphic variants

My language has polymorphic variants (the same feature as OCaml's polymorphic variants), and I want to implement flow-sensitive type refinement when pattern matching polymorphic variants. Here are ...

langdev.stackexchange.com

Alexis King @lexi-lambda.bsky.social · 2y ago

got to write this extremely fun answer on langdev stack exchange this evening and man I love Daan Leijen so much langdev.stackexchange.com/a/4242/861

[excerpt from the linked answer that starts partway through]

When this function is called, result_location will record the address of wherever result happens to be stored on the stack. Control then yields to the enclosing continuation prompt, and some time later, the continuation is restored. Unless the stack frame for foo happens to be restored to precisely the same location, the write to *result_location will fail to update the new location of result and will instead clobber whatever now happens to be at that address.

Given this fundamental issue, most programming language implementors consider implementing delimited continuations that capture the C stack to be a complete non-starter.
Doing it anyway

Fortunately, Daan Leijen is not most programming language implementors. His audaciously-named 2017 publication Implementing Algebraic Effects in C describes an implementation strategy for delimited continuations that really do capture and restore C stack frames.

How does he do it? By simply always restoring the continuation to exactly the place it was captured from, of course! In § 4.3 Resuming, Leijen describes his implementation strategy:

Alexis King @lexi-lambda.bsky.social · 2y ago

learning that the iOS app for this website does not allow me to receive push notifications for replies but not follows. cool cool

Alexis King @lexi-lambda.bsky.social · 2y ago

I guess I will try posting here: I’ve finally given in and published a small mountain of random bits of racket code I’ve had sitting on my hard drive for ages but haven’t had a good place to put it (and this is not even all of it, as I’m documenting it as I go) github.com/lexi-lambda/...

Toolbox: Miscellaneous Utilities

This library provides a collection of miscellaneous Racket utilities that I use in my personal projects but I have not felt warrant being published as a separate package. Note that this library is intentionally not published on the Racket package server, as everything in this library should be considered unstable. In projects that use it, I include this repository as a Git submodule, pinning to a specific version.

[table of contents]

Alexis King @lexi-lambda.bsky.social · 2y ago

ok can someone explain to me why like 15 people have followed me here in the past 36 hours despite this account never having made a single post. which one of you ratted me out