For some time now I’ve been oating the idea of writing a book about category theory that would be targeted at programmers. Mind you, not computer scientists but pro- grammers — engineers rather than scientists. I know this sounds crazy and I am properly scared. I can’t deny that there is a huge gap between science and engineering be- cause I have worked on both sides of the divide. But I’ve al- ways felt a very strong compulsion to explain things. I have tremendous admiration for Richard Feynman who was the master of simple explanations. I know I’m no Feynman, but I will try my best. I’m starting by publishing this pref- ace — which is supposed to motivate the reader to learn category theory — in hopes of starting a discussion and soliciting feedback.

This is an unofficial PDF version of "Category Theory for Programmers" by Bartosz Milewski, converted from his blogpost series.