Human learning loop / compilation times

Heya!

@frankmcsherry I've been noodling on timely-dataflow and differential-dataflow for months, and this week I finally got a chance to read the mdbook and go through the examples. Very fun, mind-expanding stuff! The runtime speed numbers are impressive, and I like how much TLC is put into these libraries. Thank you for all of your hard work bringing these projects to the world.

As I learn the idioms of TD/DD, I've noticed that I want to tweak the provided examples (maybe by adding a function to a pipeline, or changing the input generator to use stdin, and so on). This kind of fiddling is part of my normal hands-on tinkering-to-learn process.

Unfortunately, I haven't been able to get compile times low enough to make this learning process pleasant. I've found that compiling one of the first examples from the mdbook, with a hot incremental build cache (Rust 1.33.0), and debug mode, still takes 10+ seconds.

I looked through the verbose cargo logs, but nothing stood out to me as being a problem I could fix to speed up compilation.

I know these libraries are often described as working in "mysterious ways" -- are there techniques we could employ to speed up the compile-test-edit cycle, so that fans like me can improve our intuition of these libraries?

Thanks!

Start by reproducing the 10+ second hot incremental debug build for one of the mdbook examples using Rust 1.33.0, then inspect the verbose cargo logs to identify where compilation time is spent. The issue does not name files or tests; done would require an agreed, measurable improvement to the compile-test-edit cycle.