Immediate Feedback in Programming
Bret Victor's Inventing on Principle
Bret Victor’s talk Inventing on Principle (video, transcript) changed the way I think about computing in 2019. Inventing on Principle is partly about Bret’s guiding principle:
“Creators need an immediate connection to what they create. And what I mean by that is when you’re making something, if you make a change, or you make a decision, you need to see the effect of that immediately.”
The Edit-Compile-Run Cycle
Although Bret doesn’t use the term, programmers are deeply familiar with his principle. We’ve all worked with toolchains that introduce significant delay before you can “see” the results of a change, and we know they’re painful. Everyone wants a short edit-compile-run cycle.
But until IoP, I’d assumed that slow cycles wouldn’t materially change the output – you’d eventually get to the same place. This was wrong. I also didn’t appreciate the very small time scales involved; a 5 second delay used to seem trivial to me, but it’s still meaningfully different from a response time measured in milliseconds.
Through some very impressive custom tools, Bret shows how immediate feedback enables exploration, which then gives birth to ideas which would otherwise never see the light of day. This was an epiphany for me. Since IoP I’ve constantly been looking for better ways to code, and re-evaluating my existing processes for shorter feedback cycles. The results:
My typical Rust development workflow goes something like this:
- Write a small function that does roughly what I want
- Write a small unit test inline to exercise the function (even if it’s a private function)
- Iterate using
cargo testuntil the function is correct
- Later, “productionize” the tests if necessary
Rust’s native support for inline unit tests helps a lot here, and the excellent type system catches a lot of issues before I even run
cargo test. On the other hand, Rust’s compiler is notoriously slow and that extends to IDE tooling that depends on the Rust Language Server. I’m looking forward to Cranelift for faster debug builds.