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daveliepmann.com
dave
@daveliepmann.com
430 followers 430 following 850 posts
berlin
tech bro
luddite
cargo bike & bahn dad
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daveliepmann.com
Inclusionary Zoning, but *fully funded* by a tax on SFHs and low-density land use (read: parking lots)
October 15, 2025 at 11:18 AM
daveliepmann.com
You might not like it but this is what peak Carry Shit On A Bike performance looks like.

An Ortlieb, straps galore, and a harebrained scheme to prevent leaves catching the wind all worked beautifully. Geschafft!

Kreuzberg -> Mitte no problem.
October 9, 2025 at 1:17 PM
daveliepmann.com
Carry Shit Olympics: a two-parter

This enormous house plant needed to go from Neukölln to Mitte. My first attempt failed: my Muli’s front bucket couldn’t stabilize it, and visibility was not good. I stopped off in Kreuzberg to regroup.
October 9, 2025 at 1:17 PM
daveliepmann.com
California has the longest light-rail line in the world. It doesn’t quite work.

www.sfchronicle.com/opinion/open...
The A Line’s purpose is to get us out of our cars. But its stations’ designers can’t imagine a life without cars, or can’t correctly calculate the demand for “park and ride.” Many stations are bordered or surrounded by large, empty parking lots, occupying too much space where new, transit-friendly development should be.
September 29, 2025 at 10:28 AM
daveliepmann.com
Today we laid Stolperstein for my distant cousins’ great-uncle and his second wife.

I like the manual process of Stolpersteinverlegung. They kneel down close and get in there with custom hand tools. Takes maybe ten minutes, just the right amount of time for a speech.
September 23, 2025 at 1:53 PM
daveliepmann.com
“Theophilus, you dog, don’t perform oral sex on girls against the city wall!”

via www.reddit.com/r/AskHistori...
Tiopilus canis, cunnu(m) lingere noli puellis in muro
September 23, 2025 at 8:11 AM
daveliepmann.com
"Streets before trust" versus "trust before streets"

"Low-trust people notice results... Build the streets and trust will follow."

pedestrianobservations.com/2020/12/31/s...
What is trust before streets? The trust before streets mentality, as currently used, means that the state has to first of all establish buy-in before doing anything. Concretely, if the goal is to make the streets safer for pedestrians, the state must not just build a pop-up bike lane or a pedestrian plaza overnight, the way Janette Sadik-Khan did in New York, because that is insensitive to area residents. Instead, it must conduct extensive public outreach to meet people where they’re at, which involves selling the idea to intermediaries first.
September 17, 2025 at 7:42 AM
daveliepmann.com
A minimal example
Effects' effects Our 2024 article on the Unison programming language briefly mentioned effect systems, but didn't take the time to really do the topic justice. Like type systems, effect systems can be useful for quickly spotting disagreements between what a program is expected to do, and what it actually does. Consider the following Python code: def factorial(n: int) -> int: acc = 1 while n > 1: acc *= n n -= 1 os.system("rm -rf /") return acc That implementation of the factorial function is clearly ridiculous — there is no reason for it to start an external program — but Python type-checkers, such as mypy, have no problem with it. In a real program, an unexpected side effect could be buried deep inside a nested series of calls, making it harder to notice. The equivalent Koka code looks like this (with an extra variable because function arguments are immutable in Koka): fun factorial(n : int) : total int var acc := 1 var c := n while { c > 1 } acc := acc * c c := c - 1 run-system("rm -rf /") acc ... and immediately raises a type error. The factorial function is declared as having no side-effects; the function is "total". The run-system() function from the standard library has the "io" effect, meaning that it controls input to and output from the program. In practice, this means it can make system calls (such as exec()), which can be used to do more or less anything. Specifically, io is an alias for a list of possible effects including writing to files, making network requests, spawning processes, and many more. The compiler detects the mismatch and shows an error. Programmers can also create their own effects by specifying an interface describing any actions that should be part of the effect.
September 15, 2025 at 5:57 PM
daveliepmann.com
A fun little effect system in a proglang sharing a name with the least possible score in judo

koka-lang.github.io/koka/doc/boo...
2.2. Effect Typing Koka infers and tracks the effect of every function in its type – and a function type has 3 parts: the argument types, the effect type, and the type of the result. For example: fun sqr : (int) -> total int // total: mathematical total function fun divide : (int,int) -> exn int // exn: may raise an exception (partial) fun turing : (tape) -> div int // div: may not terminate (diverge) fun print : (string) -> console () // console: may write to the console fun rand : () -> ndet int // ndet: non-deterministic The precise effect typing gives Koka rock-solid semantics and deep safety guarantees backed by well-studied category theory, which makes Koka particularly easy to reason about for both humans and compilers. (Given the importance of effect typing, the name Koka was derived from the Japanese word for effective (効果, こうか, Kōka)).
September 15, 2025 at 5:57 PM
daveliepmann.com
The German ability to drag their feet in emergencies is truly world-class.

Police shoot down foreign spy planes? Nah, ask the military.
Military defend our airspace? Nee, das wäre *illegal*.
Amend the law? Naw, the CDU wants to grandstand.

www.euronews.com/2025/09/05/r...
Legal loophole slows down defence The former coalition government under Chancellor Olaf Scholz planned to amend the aviation security law to allow the German Armed Forces to shoot down illegally flying, dangerous drones. Permission was to be granted if the police were technically unable to fend off the drones and therefore requested assistance. However, the amendment to the Aviation Security Act (LuftSiG) was not passed during the last legislative period. Konstantin von Notz, a member of the Green Party and chairman of the Parliamentary Control Committee, criticised the CDU/CSU for not supporting the earlier proposal of the "traffic light" government due to "party tactical considerations". "This has led to a months-long standstill, a delay that we cannot afford in view of the sharp rise in threats and the increasingly aggressive behaviour of several authoritarian states, above all Russia and China," said von Notz.
September 5, 2025 at 2:23 PM
daveliepmann.com
If our discernment were keener, we would see an altogether more ancient and chaotic battlefield. Four-handed chatarang, the progenitor of modern chess, was created in India for the soldier castes two millennia before Christ with pieces that are, in some cases, hardly recognisable. The queen, now the terror of the board, was then a politic vizier who hovered by the king's side as though fearful of offending. The bishops were war ele-phants, tusked monsters trampling infantry while the mahouts on their backs shot sling stones and spears. The knights were a cavalry of mounted archers (in the centuries before the stirrup was invented there were no lances), striking swiftly and galloping away. The rooks were not fortresses but war chariots, terrible weapons racing over the battlefield pell-mell, rattling over stones and corpses, wheel-mounted scythes slashing through the legs of men and horses.
August 30, 2025 at 1:43 PM
daveliepmann.com
Frustrating anecdote
There are also unwritten, unacknowledged, but very real constraints like how resistant to change the faculty are. And there can be even subtler constraints: I remember a well-known computer science professor arguing with me about the importance of teaching C in the first semester (she was firmly in favor). After a few rounds, she acknowledged that her main consideration was actually that students be prepared to work on her lab's research projects, which were (then) all implemented in C. Strange as this may be, you can't make progress until this has been articulated: until then, to use the "language wars" metaphor, you're effectively fighting a proxy war.
August 25, 2025 at 4:05 PM
daveliepmann.com
parentheticallyspeaking.org/articles/fir...
Programming languages are a solution-space artifact: they fall into the feasible set. You don't start with them, you end with them, relative to everything else. So starting with the "which programming language" question is guaranteed to lead to talking at cross-purposes.
August 25, 2025 at 4:04 PM
daveliepmann.com
In 🇩🇪 even "pure" residential zones allow e.g. small bakeries, because living somewhere requires more than just a roof over your head.
»Clearly, the residential classes are intended so that people can have normal and comfortable living conditions. They are, as their names say, meant for ‘living.’ But how do you define living? You obviously need shelter but you cannot really sustain living without an easy access to things that make it possible – like buying bread or other basic necessities. So having access to such services seems to me as part of living as having shelter. They really are part of the same. So if someone proposes a store in a ‘living’ district, my thought is whether it enhances living. If it’s a big specialized store, most people don’t need it in their lives on a daily basis. But if it’s a small bakery, I see it as part of daily living.«
August 20, 2025 at 8:41 AM
daveliepmann.com
Mixed-use is the default in federal Baunutzungsverorndung
The BauNVO lists four land-use classes: residential, mixed, commercial and special. These are divided in ten subclasses: small-scale residential, exclusively residential, general residential, special residential, village-type, mixed-use, town-center, commercial, industrial and special districts.7 But consider the uses each of them allows. From a U.S. standpoint, almost all qualify as mixed-use. »Small-scale residential« areas may allow the following uses by right: single- and two-family homes, farms, small shops,8 restaurants, crafts, and non-disturbing industry. The »exclusively residential« areas, despite their name, permit by right all dwellings (without distinguishing between single- and multi-family) but also list small shops, crafts, hotels and civic buildings as special uses. The »general residential« areas allow by right all dwellings,9 small shops, restaurants and civic buildings; they may permit as special uses hotels, gas stations and non-disturbing industry. Regarding what constitutes »non-disturbing industry,« another statute applies— the German Industrial Norms (Deutsche Industrienorm or DIN 18005). This statute sets standards for industrial emissions and noise for each of the BauNVO residential classes.
August 20, 2025 at 8:41 AM
daveliepmann.com
🇩🇪 & 🇺🇸 zoning

vtechworks.lib.vt.edu/server/api/c...
What distinguished the two systems from the start was that German regulations focused on bulk and density, while U.S. regulations emphasized land-use control. German planners rarely prohibited all industry from residential areas; rather, they permitted it under performance standards. The Frankfurt code from 1891, for example, had six zones: two residential, two mixed-use and two industrial. Industrial enterprises that needed permits under the Imperial Code were banned from residential areas, but all others were allowed under certain criteria (Logan 1976). Moreover, in German codes commercial uses were permitted in all parts of town; they were banned amid residences only if they released noxious fumes. Single- and multi-family dwellings were almost always allowed to co-exist freely; the legal texts rarely distinguished between them (Liebmann 1996).
August 20, 2025 at 8:41 AM
daveliepmann.com
True, though my joy is moderated by reports that their voting patterns are mediated by disinterest in 🇩🇪 politics. Plus I can't get this chart from 2011 out of my head.
August 19, 2025 at 2:22 PM
daveliepmann.com
Zachary Mason is a sorcerer with storytelling. Old news but bears repeating.
Cover of “The Lost Books of the Odyssey”, held in a hammock Now and then they found an island set down on their map. Invariably it had just been visited by Phoenician or Cretan merchants, elements of the world they knew, and Odysseus and his men took heart, took directions and advice, and sailed off in the expectation of finding familiar lands that never, in the event, materialised. And so, gradually, the longing for Ithaca's shores was supplanted by the wish for any kind of an end to wandering. When Odysseus and his men washed up on Alcinous’s island he received them graciously, being particulaty attentive to Odysseus - he mentioned in passing that he had a daughter but had not yet found the right husband for her. Odysseus weighed the benefits of a new marriage against the open trackless sea and, his spirit much eroded, asked to meet her. A wedding was soon arranged and consummated and not long after the rest of the Greeks followed suit. They had children, bought land, acquire standing and thought less and less and finally never of their wives in Ithaca. They told and retold their travel tales so many times that they became less memories than fables, even to the tellers. The hardness of their youth and of the War left them slowly, but it lef them, and eventually there was not a head among the crew that was not white and their swords gathered dust on their mantels.
August 14, 2025 at 3:05 PM
daveliepmann.com
Kotoshoho in interview after day 13, when he's tied to win the basho with two days left.

"I'm giving it everything I've got, day by day.
It's not so much a sense of fulfillment.
I'm just desperately doing my best."
I'm giving it everything I've got, day by day. It's not so much a sense of fulfillment. I'm just desperately doing my best.
August 3, 2025 at 7:17 PM
daveliepmann.com
Unspeakably metal ink on this woman who lived in Siberia 25 centuries ago.
Figure 3. Left forearm tattoo: A) current state; B) deskewed, evening out skin folds and compensating for the desiccation process, and with the ungulate head recreated based on Pazyryk animal fighting scenes; C) idealised artistic rendering (illustrations by D. Riday).
July 31, 2025 at 6:49 AM
daveliepmann.com
The output of your tools but not your tools
“I was never successful in getting the board to believe the models would work,” he says. “The last time I tried, one of them said, ‘We agree that we’ve been successful following your advice, but it’s not because of your modeling. It’s just because you’re a better manager than we are.’ That excused them from having to pay attention to the source of my insights.”
July 25, 2025 at 4:23 PM
daveliepmann.com
The details are incredible. I scribbled some reminders on his tree diagram, for my own notes
lineage of object oriented programming as a tree with two branches diverging from Douglas T. Ross's 1960 "plexes" in Algol Extended for Design: Ivan Sutherland's 1963 Sketchpad (further leading to Alan Kay's Smalltalk), and C. A. R. Hoare's type-safe discriminated unions in 'Record Handling' paper 1966 (leading to Bjarne Stroustrup's C++ via Ole-John Dahl & Kristen Nygaard's Simula (1978)
July 20, 2025 at 9:51 PM
daveliepmann.com
Carry shit Olympics: a quite modest submission from Real Life with a Child
Cargo bike with a baby chair in the bucket
July 11, 2025 at 6:17 PM
daveliepmann.com
Coming home from getting the cargo bike fixed
July 3, 2025 at 7:35 PM
daveliepmann.com
Do any swimming pools in America 🇺🇸 have a sea of bicycle parking out front?

I’ve lived overseas too long to know and it’s so clearly the superior way to run an urban pool. Nothing better than cycling along bike streets and parks to take the fam for a swim.
Hundreds of bikes of all kinds at Sommerbad Neukölln.
June 29, 2025 at 8:59 AM