WTF Is a Closure?

Turns out my understanding of what a closure is exactly was almost there, but still wrong. For the longest time I thought closure was just basically another name for a function. Which it kind of is? But it's something more specific. Thanks for the learning!

I really appreciated how concise the language is in here, and how it focuses on the quick definition, gives the reader the heads up that "this is it - you can stop now", and then goes into further detail. This is really well written.