It can be hard to say whether sugar is superior or not without having a lot of experience / pain with unsugared or partially-sugared ways of doing the same thing. In this case I'd agree with you that closures could do the job just as well with hardly any more syntactic overhead. We're also in agreement with respect to libraries. The home page for Lobster mentions C++ interop, but it's unclear without digging in how straightforward that is (e.g. if one has to rebuild the compiler).