Welcome and thanks for your time here!
Puzzles are a great and fun way to learn about the intricacies of a language. "C traps and pitfalls" by Andrew Koenig, "The C puzzle book" by Feuer and "Expert C programming" by Linden are superb. So is the "Java Puzzlers" book. I remember all these books showing just a handful of code snippet to drive a point home.
What is the average length of the puzzles? Does it cover any design "gotchas"?
> What is the average length of the puzzles? Does it cover any design "gotchas"?
Thanks for your question! The chapters in the book - one puzzler per chapter - (see Nermin's comment for some more detail of the difference between the book and the Scala Puzzlers site) are 4-6 pages in length, on average. The code samples themselves are as short as possible - the principle being that if a one-line statement that seems obvious behaves in an unexpected way, that's even more puzzling than if a loooong block of code works slightly differently from what you might expect. The result is that the puzzler examples tend to be too short to get into the realm of "system design".
Some of the lessons the follow from a couple of the puzzlers could be classed as "design guidelines", but in the main the aim of Puzzlers is to teach you about a language feature, quirk or interaction that you were not aware of or - more valuable still - thought you had understood, but didn't understand completely.