You can nitpick like this about just about anything — "Erlang has immutable data? Yes, but so does Haskell etc.". That's missing the point that Erlang/OTP (and

You can nitpick like this about just about anything — "Erlang has immutable data? Yes, but so does Haskell etc.". That's missing the point that Erlang/OTP (and therefore also Elixir) is attractive because it's already a complete package. It's the intersection of a lot of different, neat technologies that becomes magical. Try to accomplish the same things in Haskell or Clojure or Go and you'll find that you simply don't have the same tools available to you, and often they cannot be built as well as in Erlang because the foundation wasn't designed for it. And there's always some piece missing. For example, you can build an approximation of supervisor trees in Go, but since goroutines cannot be killed, you're at the mercy of the runtime. (I also wonder if goroutines scale as well as Erlang's.) Similarly, no one has actually built a functional, immutable, process-oriented call-by-name-and-signature RPC mechanism for Go, so you'll have to invent your own. And so forth. As a specific example, I was recently investigating OCaml to see if someone had implemented something similar to OTP. I found a couple of promising, nascent projects, but their activity all ended around 2009. Apparently nobody is doing it, even though the language seems damn near perfect for it. Never mind distributed processes; LWT is pretty weak even as an approximation of Go's goroutines. > [downtime] This doesn't need to be a language feature ... Erlang's live code replacement changes how you mentally think about versioning, I think. Instead of designing every piece of your infrastructure to transparently transition to a new version — using load balancers, multiple processes accept()ing on the same port, and so forth — you get a first-class language construct. This also opens possibilities beyond code deploys, such as temporarily injecting tracing into a running program. Also not often mentioned is how powerful it is to be able to connect to a running process and run the REPL inside it. (Ruby comes close here, but it's never been something you get for free.)