Have you ever tried programming with a language that uses musical notation? What about a language that never runs programs the same way? What about a language where you write code with photographs?
All exist, among many others, in the world of esoteric programming languages, and Daniel Temkin has written a forthcoming book covering 44 of them, some of which exist and are usable to some interpretation of the word “usable.” The book, Forty-Four Esolangs: The Art of Esoteric Code, is out on 23 September, published by MIT Press.
I was introduced to Temkin’s work at the yearly Free and Open source Software Developer’s European Meeting (FOSDEM) event in Brussels in February. FOSDEM is typically full of strange and wonderful talks, where the open-source world gets to show its more unusual side. In Temkin’s talk, which I later described to a friend as “the most FOSDEM talk of 2025,” he demonstrated Valence, a programming language that uses eight ancient Greek measuring and numeric symbols.
Temkin’s intention with Valence was to emulate the same ambiguity that human language has. This is the complete opposite of most programming languages, where syntax typically tries to be explicit and unambiguous. “Just as you could create an English sentence like, ‘Bob saw the group with the telescope,’ and you can’t quite be sure of whether it’s Bob who has the telescope and he’s seeing the group through it, or if it’s the group that has the telescope,” he says. “What if we wrote code that way so you could write something, and now you have two potential programs? One where Bob has a telescope and one where the group has a telescope.”
How Esoteric Languages Spark Creativity
Creating a language or an interpreter has often been the proving ground of many engineers and programmers, and esoteric languages are almost as old as nonesoteric ones. Temkin says his current effort has a lot to do with AI-generated code that seeks to do nothing but provide seemingly straight solutions to problems, removing any sense of creativity. Esoteric languages inherently make little sense and frequently serve little purpose, making them conceptually completely counter to AI-generated code and thus often not even understood by them—almost the code equivalent of wearing clothing to confuse facial recognition software.
While the syntax of esoteric languages may be hard to understand, the actual programming stack is often wonderfully simple. Temkin believes that part of the appeal is also to explore the complexity of modern programming. “I come back a lot to an essay by Joseph Weizenbaum, the creator of the Eliza chatbot, about compulsiveness and code,” he says. “He described ‘the computer bomb,’ the person who writes code and becomes obsessed with getting everything perfect, but it doesn’t work the way they want. The computer is under their control. It’s doing what they’re telling it to do, but it’s not doing what they actually want it to do.”
“So they make it more complicated, and then it works the way they want,” Temkin adds. “This is the classic bind in programming. We command the machine when we’re writing code, but how much control do we really have over what happens? I think that we’re now all used to the idea that much of what’s out there in terms of code is broken in some way.”
Temkin explored the idea of control in his language Olympus, where the interpreter consists of a series of Greek gods, each of which will do specific things, but only if asked the right way.
Temkin’s Olympus language includes an interpreter consisting of Greek gods, which must be asked to do things in the proper way. Daniel Temkin
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