[valenterry]

> The application programmer writes sequential code, all concurrency is hidden away in the behaviour;

Yeah, until the business problem itself involves inherent concurrency, which usually happens much faster than people think. Or until I, as the non-expert, want to dig in to make changes or debug a problem.

This distinction into "expert" and "lowlife (SCNR) using the expert abstractions" is really one that doesn't hold in practice most of the time.

I think it's much better to embrace that concurrency is a cross-cutting-concern and reality is that it can happen on any level, so the language should better support reality.

[jeremyjh]

I think you're talking about two different things. When they say concurrency is hidden away, I think they mean the programmer isn't dealing directly with locks/mutexes. They are also lying, since async functionality like `handle_cast` is built into the `gen_server` behaviour and every caller is calling either `gen_server:cast` or `gen_server:call` depending on whether or not it is going to block on a response. Whenever you invoke async behaviour concurrency will invade all the domain logic and can't be ignored.