Free public beta until December 4, 2026: every course is open, no card needed. After that, the first chapter of each course stays free and full access is a one-time $39 ($19 for up to 100 founding members chosen for helpful feedback). Your progress is kept. How the beta works

call stack

The last-in, first-out pile of frames for the calls in progress; only the top one runs.

Examples

main calls total, which calls round: three frames, and round returns first.