In pure functional language, you are not allowed to tinker around with the state, So the state go into your function, something should happen and the… - Joe Armstrong

Composing computation. Why do we do compose computation? Because We want to make reusable things out of small things. We take small things to make bigger things.

When I'm writing a program, my approach is to "write a bit" and then "test a bit." I start with a small module with few functions, and then I compile it and test it with a few commands in the shell. Once I'm happy with it, I write a few more functions, compile them, test them, and so on. (page 60)

deployment is a problem because even if somebody made an open source privacy application, it needs 50 million users to take off. Apple and Google and everybody have dominated this way of deploying something to hundreds of millions of people [...] the first one to get a hundred million users wins basically.