The beauty of software is that you can pretend the rest of the word doesn't exist while you are writing a single function. You can pretend that data is passed i

The beauty of software is that you can pretend the rest of the word doesn't exist while you are writing a single function. You can pretend that data is passed in, transformed, and passed out. You may pretend there are no side effects, or something like that. But when you pretend this way, you make many assumptions. It is good to have a shared vocabulary for these assumptions.