I know my mind is decidedly poisoned when I could follow the type definitions perfectly, and they reminded me of certain types I have written myself… ah, TypeScript, what have you done to me…
Deep diving into lib.d.ts and DefinitelyTyped dealing with the weird boundary space between poorly typed JS and strongly typed TS can teach a lot these days.
Also, being able to recognize the Peano S-function on sight (and thus uses of Church-Peano numbers) is a fun part of that wizardry. (Maybe not necessary to remind the usefulness of the Lambda Calculus canon on a site named after one of the most famous combinators.)
