Valen experiments with a borrow checker that walks functions backwards

Instead of scanning forward, this experimental language’s safety pass walks a function from its end toward its start. It tracks references that will be used later, then rejects mutations that would invalidate them before those uses; the author also explains how the approach handles loops.

The write-up is a detailed look at a new compiler algorithm, not a settled design: Valen is still experimental, control-flow cases and closures remain unfinished, and the author has not benchmarked the claimed speed advantage. In the small HN thread, the author invited people to try to break the algorithm, while a reader offered encouragement. HN discussion: https://news.ycombinator.com/item?id=50140383