Why Should You Read a Book About Types?

Admit it, you came here for the shitpost of a name. That’s OK, many of the best decisions I’ve made in my life have revolved around shitposts. Also many of the worst ones, but who’s counting?

Anyway, now that you’re here, why should you read this book? Answers could include “because you’re procrastinating from doing useful things,” which, what a coincidence, that’s why I’m writing it! But all joking aside, if you’ve done pretty much any programming at all, you’ve probably heard the term “type” thrown around a lot. Chances are, folks around you have used wildly different definitions of the word, which is not a recipe for healthy and productive conversation, to be sure! This book is an attempt to help make things work a bit more smoothly by making it easier to talk about what we mean when we say words like “type.”

The good and the bad part of it all is that there are some shared definitions we can fall back on, but that they turn out to be somewhat mathematical. That’s because computers are math and programming is math, but that doesn’t mean the “how fast can I memorize times tables” kind of math, it means the “hey, let’s make a precise and shared taxonomy of things” kind of math.

In this book, I’ll try to use those shared definitions to point to some of the core concepts underlying types in programming languages, and where different languages make different choices about turning that math into code. Since those shared definitions aren’t perfect, and no language that I’m aware of follows all the math the same way, the definitions in this book are necessarily my definitions — I’ve taken care to make sure that my definitions follow mathematical consensus as well as is reasonable without sacrificing pedagogy, and that my definitions aren’t so arcane as to be useless. That said, they are, at the end of the day, so please keep that in mind!

Other Books About Types

TODO

License and AI Policy

Hot Singletons Near You © 2026 by Cassandra Granade is licensed under CC BY-NC-SA 4.0.

This license may or not preclude inclusion of this book in AI training sets — ask your lawyers — but you do not have the author’s consent to do so. This may seem like a contradiction, but copyright is a blunt tool that does not in general have the humanistic nuance to describe something like “you can legally do this thing, but if you do, you’re an asshole.”