Algorithms
This category collects posts where we dig into algorithms and how APL expresses them. You’ll find worked examples covering sorting and ordering, performance tuning, real-world methods like D’Hondt apportionment, and classic puzzles like Krypto, all explored through actual APL code, benchmarks, and step-by-step reasoning.
In February 2026, the APL Challenge quietly launched its next round on a rewritten stack. The previous infrastructure was retired and replaced by... Read
Background The stencil operator ⌺ was introduced in Dyalog version 16.0 in 2017. Recently we received some feedback (OK, complaints) that (a) stencil does... Read
- In: Algorithms, APL Language
Lexicographic Ordering Lexicographic ordering is what the APL primitives ⍋ and ⍒ provide: ⎕io←0 ⍝ ⎕io delenda est ⎕rl←7*5 ⍝ to get... Read
- In: Algorithms, Recreational
In the 2016 Year Game, the task was to generate the numbers 0 to 100 using APL primitives and the digits 2 0 1 6 in that order. For example, 20=16 ×2016... Read
Finally, the last accessory I ordered for my Raspberry Pi Zero (that’s the little red thing behind my keyboard) has arrived – an Acer 43″... Read
- In: Algorithms, APL Language, CXO, Raspberry Pi, SharpPlot
Earlier this week I collected some reaction timer data on my Pi using the BBC micro:bit as an input device. I only produced an “ASCII art” chart at... Read
- In: Algorithms
These exercises are designed to introduce APL to a high school senior adept in mathematics. The entire set of APL Exercises has the following sections:... Read
- In: Algorithms, APL Language, Musings
⎕io←0 throughout. I was re-reading A Mathematician’s Apology before recommending it to Suki Tekverk, our summer intern, and came across a statement... Read
- In: Algorithms, APL Language
Andy reported that in the shuffle QA some functions take a long time: m9249 “4½ days so far” rankop 21.5 hours... Read
- In: Algorithms
The halting problem is the problem of determining, from a description of a program and an input, whether the program will finish running or continue to run... Read
A message in the Forum inquired on sorting strings in APL with a custom comparison function. First, sorting strings without a custom comparison function... Read
- In: Algorithms, APL Language
I started composing a set of APL exercises in response to a query from a new APL enthusiast who attended Morten’s presentation at Functional Conf,... Read
- In: Algorithms, APL Language
Part I of this post was concerned with the development speed and execution speed of magic functions and should be read before this post. Benefitting from... Read
- In: Algorithms, APL Language
A magic function is an APL-coded (dfn) computation in the C source of the interpreter. For example, some cases of ∧.= are coded as... Read
- In: Algorithms, APL Language
Karen Shaw started the ball rolling (hearts afluttering?) by asking Jay Foad to come up with a one-liner for St. Valentine’s Day; he then solicited... Read
This post is the continuation of the series where we examine some of the problems selected for the 2014 APL Problem Solving Competition. In this post... Read
This post is the continuation of the series where we examine some of the problems selected for the 2014 APL Problem Solving Competition. In this post... Read
This post is a continuation of the series where we examine some of the problems selected for the 2014 APL Problem Solving Competition. I’ll start by... Read
- In: Algorithms, APL Language
Acknowledgments Morten Kromberg is the other co-author of this text but the blogging software prevents his being listed as such. We are indebted to Jay Foad,... Read
The most obvious expression for computing π in APL is ○1. But what if you can’t remember how ○ works, or your O key is broken, or you feel like... Read
The winners of the 2014 APL Problem Solving Competition were recognized at the Dyalog ’14 user meeting and had a chance to share their... Read
- In: Algorithms, APL Language, Dyalog '14
Recent versions of Microsoft Windows support touch screens, which of course means that applications can respond to events originating from touches. Microsoft... Read
- In: Algorithms, CTO, Raspberry Pi, Robots
As the odour of fried electronics dissipates in the air, I’m unexpectedly afforded the opportunity to write this blog post a day or two earlier than... Read
- In: Algorithms, APL Language, CTO, Raspberry Pi, Robots
Last week the ‘bots were busy preparing for the J Language Conference in Toronto, where they made their first public appearance together. Upon returning... Read
- In: Algorithms, APL Language, CTO
‘Bots are off limits this week so here is a story from this year’s Iverson College – a fantastic week spent in the company of a wonderful mixture of... Read
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