Functional Programming by Example - Side Effects

Long time no see! I want to continue my explorational series of functional programming with side effects.
After doing some research I came across this excellent talk by Kris Jenkins about functional programming.

I my opinion he does an outstanding job in explaining the meaning of side effects and functional programming in general.
So instead of writing a long blog post, I leave you with this talk. Money quotes:

Hidden inputs and outputs are called ‘side effects’

Functional Programming is eliminating & controlling side effects

Kris Jenkins

Let me know if things in this talk need clarification!