Multicore OCaml works using a thread-safe generational garbage collector. Each domain (i.e. thread) gets its own minor heap, and the major heap is shared. Each

Multicore OCaml works using a thread-safe generational garbage collector. Each domain (i.e. thread) gets its own minor heap, and the major heap is shared. Each heap is GCd independently. The domain-level minor heaps are restricted so different domains can't write to each other's minor heap. And the shared major heap is protected with more bookkeeping. More details in https://kcsrk.info/multicore/gc/2017/07/06/multicore-ocaml-gc/ https://kcsrk.info/multicore/gc/2017/07/06/multicore-ocaml-g... Scala of course just uses the set of GCs that are available on the JVM. OCaml's GC has an advantage in that it's optimized for quickly creating and collecting many small objects–perfect for functional programming. But some advanced JVM GCs probably come close to that. The new effect system is basically 'resumable exceptions'. An effect is declared somewhat similarly to an exception. When the effect is 'thrown', it is handled by the nearest effect handler up the callstack. The difference from an exception is that once (if) it is handled, it actually resumes at the exact position in the code where it left off, not in a continuation created by a closure which is effectively what Scala and every other userland effect system does.