> Other than say, Erlang, I'm not aware of many alternatives which provide a) ultra-cheap coroutines (10,000 coroutines? fine!), b) an I/O system which is seaml

> Other than say, Erlang, I'm not aware of many alternatives which provide a) ultra-cheap coroutines (10,000 coroutines? fine!), b) an I/O system which is seamlessly integrated with that concurrency system (and in a totalitarian manner at that; if you're using Go, you're using its event-based I/O scheduler, no exceptions), and c) a rock-solid runtime. GHC Haskell.