Semicolon is out. It’s an iPhone and iPad app for practicing the parts of programming that interviews still test.
More and more code gets written with an LLM’s help, and I don’t expect that to change. A company can assume you’ll use a model, but it still needs someone who can read what the model wrote, find the bug in it, and decide whether it’s any good. That takes a solid grasp of the fundamentals, and fundamentals fade quickly once you stop typing them out yourself. Semicolon is a way to keep them sharp.
Figuring out what a seasoned developer should know is a hard problem. I talked to many other senior software engineers to come up with this list of skills. They demonstrate competence, and they’re the fundamentals that help you work with LLMs more effectively.
What’s in it
There are eight courses with 24 sections each: ARM64 assembly, Python, Rust, Kotlin, SwiftUI, discrete math, design patterns, and data structures and algorithms.
I picked them because each one shows you understand something essential.
Assembly and Rust are about what the machine is doing. In assembly you work with registers and memory directly. In Rust you have to understand ownership before the compiler will let you do anything. I chose ARM64 because that’s the architecture in phones and in Apple silicon.
Python is what most people reach for when they work with a model, and it’s a common language for interviews.
Data structures and algorithms, discrete math, and design patterns are the material interviews have always drawn on. They’re also the vocabulary you use to talk to a model about code and to judge what it gives back.
Kotlin and SwiftUI cover the two mobile platforms. I expect local models to end up running on phones over the next few years, so these are the languages you’d use to build for them.
How it works
Every exercise uses real code. Depending on the lesson, you might pick the right answer, fill in a blank, fix a bug, predict what a snippet prints, or write a function. After each answer you get an explanation of why it’s right or wrong. A concept page is one tap away if you get stuck mid-exercise. If you already know a section, you can test out of it with a timed challenge.
Lessons are short, so a lesson a day is realistic.
Price
ARM64 assembly and Python are free. A single purchase of $24.99 adds the other six courses. There’s no subscription, no ads, and no account to create. Your progress stays on your device. There are no hearts or lives and no streaks to protect.
Try it
Semicolon: Learn to Code on the App Store
If you try it and like it, a rating on the App Store helps a lot. If something breaks or a lesson is wrong, the support page is the way to reach me. More about the app is on the Semicolon page.