May 1, 2026
Ctrl-Alt-Drama
A Letter from Dijkstra on APL
Dijkstra roasted APL as a ‘cult,’ and the comments are loving the chaos
TLDR: A newly resurfaced letter shows Dijkstra dismissing APL as something like a cult, saying people avoided it because of what it did to its fans. Commenters instantly turned that into a fight over whether APL was misunderstood genius, unreadable chaos, or both at once.
A decades-old letter from famed computer scientist Edsger Dijkstra just got dragged back into the spotlight, and wow, the internet did not keep calm. In the letter, Dijkstra basically says APL — a famously symbol-heavy programming language — inspires near-religious devotion, and that many people avoid it because they don’t want to become like its biggest fans. Ouch. He also throws in a very elite-sounding jab that a “proper” language should be teachable with pencil and paper, not just shown off on a machine. That alone was enough to send commenters into full popcorn mode.
The reactions were split between “he kind of had a point” and “this man absolutely did not get the vibe.” One commenter confessed APL is the only language they’ve ever literally dreamed about — which, honestly, does not beat the cult allegations. Others rushed in to defend it, arguing Dijkstra may have been reacting less to the language itself and more to the miserable old hardware of the time. One person wondered if modern screens and Unicode symbols would’ve changed his mind, while another compared APL’s reputation to Perl’s: weird-looking, intimidating, and doomed by first impressions. Then came the counterattack: computers are supposed to let us think in new ways, so why worship pen-and-paper purity? And for extra spice, someone pointed to Russ Cox using an APL-like tool for Advent of Code, a reminder that this supposedly alien style still has fans in high places. In other words: an old letter became a fresh comment-war about whether unusual tools expand the mind — or just melt it.
Key Points
- •Roger K.W. Hui republishes a 1981 letter in which Edsger W. Dijkstra criticized APL and described its users as unusually tied to implementation and terminals.
- •Dijkstra argued that APL’s printed or written form was not an adequate medium for its propagation and suggested this contributed to the language’s relative isolation.
- •The letter was addressed to Dr. A. Caplin at Burroughs in Croydon, Surrey, United Kingdom, and includes Dijkstra’s note that he was signing with his left hand due to a broken right arm.
- •Hui argues that Dijkstra’s comments are ironic because Ken Iverson created Iverson notation as a communication system before it was implemented on computers as APL.
- •Hui contends that non-trivial work can be done in APL without executing it on a computer, while also arguing that executability is useful in teaching and in checking formal reasoning.