hey great tutorial! really easy to go through, super helpful.

My only suggestion : it would be great to have a small reference/cheatsheet/table to convert equivalent data structures and other syntactic details from closure to other languages. I found myself scrolling back up a lot to remember what "def" meant (coming from python this was confusing), whether "vector" was a dict or a list, etc. It interrupted the reading for a few seconds every time until "ah ha!" I found it.

I remember spending about 50% of my time learning Mongo syntax just checking out their mysql <-> mongo syntax table - I assume most people checking out your tutorial will have experience with some previous form of programming (like me).