When I was learning Python on Udacity’s Python course, I worked out solutions to the problem sets on paper. That’s when I do my best, 100% focused thinking: with a good pen and a nice notebook.

It’s still the most enjoyable programming experience I’ve had.

Lisp dialects are usually nice enough to write on paper. Because whitespace between list elements is never important in classic Lisp, you can break lines wherever it makes most sense visually to do so. Plus, the referential transparency means that you can write on loose sheets without any specific order (although many Lisp compilers do read top-to-bottom in practice).