The importance of (and tricks for) doing proofs about code you’re writing as you write it:

This is a brief write-up of a trick I learned that helps me write code faster and more accurately. I say “trick”, but it’s really something I started to do without noticing as I moved further into my career.

When you’re working on something difficult, sketch a proof in your head as you go that your code will actually do what you want it to do. A simple idea, but easier said than done: doing this “online” without interrupting your flow takes a lot of practice. But once you get really good at it, you’ll find that a surprising amount of the time your code will work on the first or second try. It feels a little magical.

(via John Regehr)