[monopede]

You can build a library for doing Erlang-style programming, but there are lots of features that you can't reproduce.

(1) In C++ you may get hard crashes, so to get reliability you need to use high-overhead OS processes. Erlang allows you to hundreds of thousands (yes, really) of processes because they are really lightweight (76 words + heap/stack). Also, copying within the same address space has much lower overhead (no system call/context switch) and serialisation is much simpler.

(2) Because of immutable data you can do have nice fault tolerance as follows. Imagine you have a request handler function that takes a state and a request. However, the request is malformed or triggers a bug in the handler. In a language that doesn't enforce immutability you have to restart the handler process because the state may be in an inconsistent form. In Erlang you would just discard the request (or send an error message) and handle the next request with the unmodified state.

(3) Pattern matching makes receiving a message very convenient.

I probably forgot a few things, but this gives you an idea.