Knowing and Doing

Today is my birthday. I won't tell you how old I am, and I promise not to pull a Gwyneth Paltrow. Trust me; no one wants that.

I do not have a birthday essay planned, or any deep reflections on the passing of time. Birthdays have never been times of deep reflection for me. As I grow older, they have not yet started to mean anything different to me, even as I realize that they will be fewer and fewer. I mostly think of them as a time to relax, think on the good things in my life, and get on with living it.

It's just as well that I have no birthday essay planned. My friend Daniel Steinberg wrote about his birthday a few weeks ago, and I cannot improve on what he said. Daniel turned 65 this year, a milestone in a culture that emphasizes youth. Daniel, though, is still learning and teaching us what he learns with his books and presentations. He notices now that the other attendees at the conferences where he speaks are much younger than he is:

I'm the same age or older than their parents.

I'm sure they see me as old.

For the most part, it is much worse in my head than in theirs.

I know this feeling. I work with college students every day. I'm older than all their parents now, and probably not that much younger than a few grandparents. I'm sure they seem me as old, but how much of that is in my own mind?

I have a few years before I reach sixty-five, but it's close enough that I've been told I should start thinking about retirement and investment accounts and a different kind of life. But I'm of the same mind as Daniel: "Retire to do what? Travel? Do things I'm interested in? I do all that now." The life of an academic, at least one fortunate enough to have found a steady, secure position, is good: we read, write, and teach the thing we love. As long as I can do these things well enough and enjoy them, I will.

2024 has been, in some ways, an eventful year. My dad died unexpectedly this summer. A couple of months later I learned that one of my college mentors died around the same time. Those were times of reflection for me. On a more uplifting note, my wife and I got to visit our daughters in Boston this spring and spend time with our favorite people in the world. Later we took a 48-hour break mid-summer to visit Minnesota and ride the full length of the Sakatah Singing Hills State Trail and back in one day. Riding 85 miles gives you plenty of time to enjoy the beauty of the world. (That's a blog post I've been meaning to write for three months...)

This is a milestone birthday for me, too, as counted by the rest of the world. However, a few years ago, I started enumerating my birthdays in hex (base 16), a shrewd move for a computer scientist. That means I am still comfortably in my 0x30s, young enough to keep doing the things I love to do.

Andrej Karpathy loves his calculator, and I like his post about how he loves his calculator. I was planning to quote the beginning of one paragraph as a teaser, but I could not decide where to clip the passage. Each sentence is worth seeing. I hope he does not mind that I show you the entire paragraph with encouragement to read the entire post:

Let's put this in perspective to the technology we increasingly accept as normal. The calculator requires no internet connection to set up. It won't ask for bluetooth permissions. It doesn't want to know your precise location. You won't be prompted to create an account and you don't need to log in. It does not download updates every other week. You're not going to be asked over and over to create and upgrade your subscription to the Calculator+ version that also calculates sine and cosine. It won't try to awkwardly become a platform. It doesn't need your credit card on file. It doesn't ask to track your usage to improve the product. It doesn't interrupt you randomly asking you to review it or send feedback. It does not harvest your information, for it be sold later on sketchy data markets, or for it to be leaked on the dark web on the next data breach. It does not automatically subscribe you to the monthly newsletter. It does not notify you every time the Terms of Service change. It won't break when the servers go down. The computation you perform on this device is perfectly private, secure, constrained fully to the device, and no running record of it is maintained or logged anywhere. The calculator is a fully self-contained arithmetic plugin for your brain. It works today and it would work a thousand years ago. You paid for it and now it is yours. It has no other master. It just does the thing. It is perfect.

You paid for it, and now it's yours.

My favorite pieces of software and favorite creators of software embody this ideal, at least as much of it as they can given the constraints of the modern tech world. Audio Hijack from Rogue Amoeba comes to mind and Acorn from Flying Meat come to mind.

That said, I loved calculators long before the web existed at all. Young Eugene had many hours of pleasure noodling on a calculator, playing with numbers. I first learned about rounding errors and limits by typing in a number and repeatedly hitting the square root key until the display showed a 1. I computed batting averages and winning percentages for my favorite teams and players. Eventually I was computing chess ratings by hand, until I sensed what a computer program could do for me. That would become the first program I ever wrote out of passion.

Even after learning to program, I never really lost the joy of tinkering with an old handheld calculator. It just does its thing. It is perfect.

Today I learned that HTML's <strike> tag has been replaced by two tags, <del> and <s>.

I knew that <strike> had been deprecated but had never needed to learn its replacement, or that a replacement even existed. I used it occasionally back in the days when dinosaurs roamed the web, but only rarely since. When I used it, browsers always displayed the text as expected, so I took the easy route and kept on using it.

Two things have changed since the last time I used <strike>. I taught web development for the first time last fall and decided that I wanted to write modern, compliant HTML and CSS whenever possible, both as a good example for my students and as a way to up my web game to the 2020s. The second change was more abrupt: I used <strike> today and encountered a browser that no longer supports it.

At first, I figured I'd just write a little CSS to simulate the desire behavior with a class. That's the sort of thinking that knowing CSS makes possible. But I also know that HTML includes a remarkable set of elements and that we should prefer native HTML whenever possible. So I looked <strike> up in the MDN documentation. As they say, RTFM! The documentation enlightened me.

The two replacement elements have different semantics for the act of striking through text:

• <del> is for information that has been deleted
• <s> is for information that is no longer correct

Now I have to think about which of these I mean when I decide to strike text in a page. But I don't mind this at all. I'm a big fan of HTML's semantic elements. What we write should express our intent, and these elements help us encode meaning and structure directly into our documents.

Even better, browsers and screen readers can use the structure of a document to present it more accurately, which means that using semantic elements makes our web pages more accessible to visually-impaired readers.

Further, using semantic elements also makes our pages more ready for futures that don't exist yet. I love the story in this blog post about how pages written with semantic markup displayed properly on the Apple Watch, even though they had been written well before the product launched. (If you'd like to jump directly to that story in the post, search for "NEW TYPES OF DEVICES".)

To bring my story to a close: I decided to use a <del> tag in the page I was writing for my students. The text in question was a bad idea, so I marked it as deleted. Whenever I open up this page in the future, the markup will include a hint as to why the text has been stricken.

First from French writer André Gide, in Le Traité du Narcisse (1892):

Everything has been said before. But since nobody listens we have to keep going back and beginning all over again.

Every teacher knows how Gide feels.

Then from Bruce Springsteen, in a New Yorker interview I've lost track of:

This music has not been heard at this moment, in this place, by these faces. That's why we go out there.

Springsteen said that when asked how he could still sing "Born to Run" with so much energy after decades of performing. I think something similar to myself on many teaching days. I love the thing I am teaching and, even though it's old hat to me, it's new to my students, and I want them to love it, too.

I've always been a sucker for quotes that aren't about teaching, or programming, but could be. Making that sort of connection can motivate me on those days when I need a little pick-up.

But I also realize that making connections to other disciplines is a big part of how we teach or write programs at all. Metaphors are everywhere in both. Consider this line from Zach Tellman in a recent issue of the newsletter about his book in progress, "Explaining Software Design":

The queue is a useful metaphor because it makes us ask useful questions.

We create analogies and metaphors because they help us ask useful questions. They help us see our own objects of study, or own activities, in a new way.

I guess this is my way of saying that I'm okay with my irrational fondness for applying quotes out of context to my own world. Doing so occasionally helps me ask better questions. Even when they don't, I get to smile.

I decided to scratch an itch this afternoon with a trivial bit of code.

My students use a homegrown system to submit their work in my courses. After the assignment is due, I scp the assignment's directory from the server to my machine and add it to the course repository. This directory contains one subdirectory for each student, holding their individual submissions.

I use a few scripts and a couple of manual steps to review student work, write up notes for them, and send them the reviews. Most of the scripts iterate over the subdirectories. For many tasks, it is simplest to assume one subdirectory for each student in the class.

I do all this work on two machines, one at home and one in my office. I use git to keep the repos in sync.

It's always been the case that, for any given assignment, one student might not submit anything. That's not a problem when I'm running my scripts on the same machine where I downloaded the submissions. But on the other machine, which gets the data via a git push or pull, the empty student subdirectories — poof! — disappear. git tracks files, not folders.

I'm sure there is a mechanism somewhere in git for handling this sort of thing (isn't there a mechanism for everything somewhere in git?), but in the past I've done it by hand: I glanced at the subdirectory listing and, when I saw an empty folder x, I typed touch x/_nosubmit. When there is only one empty student folder, this is quick and easy. But as the number of empty student folders goes up, it becomes tedious. Two developments over the last few semesters have driven the tedium to an uncomfortable level.

First, I've noticed that the number of students who miss the initial submission deadline rising. There are a variety of reasons that this is happening. I am happy to work with students who need to submit later, but this means more empty directories when I make my first pass reviewing submissions.

Second, I am trying to give students many more low-stakes opportunities to write code and get feedback. Instead of grading one assignment per week, I may now be evaluating submissions for three different tasks.

Put these two factors together, and I rapidly grew tired of scanning subdirectory listings and touching empty files.

Sounds like time for a new command. At first I tried to do it in a single line of bash, using xargs, but that didn't work. (My intuitions about xargs often fail me.) So I wrote a simple for loop:

    for entry in $(find "$1" -type d -empty)
    do 
        touch "$entry"/_nosubmit
    done