Swift Playgrounds on MacOS performs badly, spinning up the fans and working the CPU

Using the basic "Learn to Code 1" playground results in the MacBooks that I've tested on, including a 2020 MacBook Air, working far harder than I'd expect. The fans spin up and the CPU usage increases more than I'd expect. The performance settles down if I leave the application running, I see the high load whenever I type and change the program. The app is compiling some Swift code and displaying a fairly simple game interface to show the results. What can account for this poor performance on a capable machine?