This is a post going over the basic concept of
defining objects through **Universal Properties**,
in Category Theory, with explanations and examples in Haskell.

- 2020年12月31日
- 8 分

(Basic) Universal Properties in Haskell- 2020年12月07日
- 7 分

(Un)fold as (Co)algebraOne cool thing about lists is that they have canonical ways of consuming and producing them: folds, and unfolds. It turns out that these are canonical, in that folding and unfolding functions are themselves isomorphic to lists. In this post, we’ll explore why this is true.

- 2020年10月02日
- 9 分

Categorical GraphsThis post is a basic introduction to the idea of Categorical Graphs, or just the standard theory of Graphs, developed through the lens of Category Theory, and generalized in the obvious ways that follow through that lens. This is just an introduction mainly because this theory doesn’t seem to have been developed very far yet, and I haven’t been able to develop it that much independently so far. I think I have a good grasp on some very basic ideas here, and wanted to present them while they’re still fresh in my head.

- 2020年09月09日
- 10 分

Recursive Types as Initial AlgebrasRecently (well, more like a month ago), I came across this interesting observation: In my head, I immediately jumped to the notion of Algebras in Category Theory. I had recently studied that notion, found it quite interesting, and was very happy to see this observation, because it was actually quite obvious to me thanks to what I’d recently learned. The goal of this post is to unpack that tweet, and then explain why that observation is true.

- 2020年08月30日
- 17 分

Encoding the NaturalsIn this post, we’ll cover 3 ways I know of encoding the natural numbers $\mathbb{N}$ in your standard functional language with recursive types and polymorphism. At least, these are the 3 most generalized ways of doing it. As we’ll see, some common encodings are just specific cases of a more general encoding. Prerequisites Some familiarity with defining data types in a functional-esque language might be helpful, but shouldn’t be strictly necessary.

- 2020年08月17日
- 14 分

Empty vs NonEmpty GroupsThe usual definition of a Group excludes empty groups by definition. There are alternate definitions of a Group that allow us to include the empty set, and which are quivalent to the normal definition in all other cases. This post explores this alternate definition, and the resulting differences with the normal concept of a Group. What is a Group? A Group is one of the most important structures in abstract algebra.

- 2020年06月18日
- 7 分

Monomorphisms vs EpimorphismsThe concepts of

*monomorphism*and*epimorphism*are very important in*Category Theory*. I always had a hard time remembering which one was which until I thought about a good mnemonic.