> It's been a while but I thought the point was to experiment with static typing of XML transformations, but ultimately type inference complexity results hit a wall

Type inference for set theoretic type systems is expensive and that has not changed. It is not surprising either: inference is harder or undecidable in more expressive type systems.

We address this by providing reconstruction based only on patterns, guards, and return types. Other than that, inference is not a major limitation to us, given you don’t need to declare types today anyway.