> BTW, my other assumption is that a puzzler should show common idioms, as a learning tool

Definitely. We'd like to avoid bad style and teach good habits. Another goal is to allow puzzlers to be presented and glanced over/understood in a couple of minutes during a presentation.

While everyone seems to like [#5](http://scalapuzzlers.com/#pzzlr-005), for instance, it already pushes the boundary of what people can understand while glancing it over. Hence the desire to keep things puzzling but - at first sight, at least - short and simple.