Monoid is fairly easy to understand, even if you’re just starting out in functional programming. First, you need to understand what a Semigroup is. The Cats definition is very accessible:

A few times I’ve fallen into the trap of making incorrect assumptions about what a type is based on how I read it in my head. Most recently, this happened with the asRight and asLeft wrappers of cats.Either.

The name of flatMap might trick you into thinking that it is the same as flatten followed by map. But it’s exactly the other way around: it’s map followed by flatten.

According to the documentation for java.nio.ByteBuffer.wrap(array):

Say you want to implement a function add1 that takes a list of integers and adds 1 to each one, so that:

I recently realised that ambiguous argument naming has been a major obstacle for me building intuition about how foldRight works in Scala.