[ajarmst]

I liked his introduction to Category Theory enough to buy the extremely well-done hardcover edition:

https://www.blurb.com/b/9621951-category-theory-for-programm...

The only introductory treatment of Category Theory for non-specialists that I’ve encountered that even competes with it is Spivak’s “Category Theory for the Sciences.” For the curious, Eugenia Cheng’s books for lay audiences are excellent for getting a feel of the power and value of the Category Theoretical approach.

Category Theory is somewhat unique in being a recently developed area of advanced maths that is nevertheless approachable with only modest formal training. Because it maps so well to much of the theory and practice of functional programming, most programmers with even a little interest and familiarity with that will be able to engage with the fundamentals, and Milewski does a masterful job of introducing it to that audience.