Reducers -- a tool for handling state changes -- help engineers manage complexity in their applications. But why is this such a great tool for managing this complexity? In this post, we'll figure out the underlying power of reducers by exploring monoids on functions and learn some more formal terms in the process. All code examples will be presented in OCaml, ReasonML, TypeScript, Haskell, and Swift.

Forming the set of equivalence classes is called “modding out” or “quotienting by” the equivalence relation.