[s3cur3]

Elixir (really, the Erlang VM it's built on) is designed for highly concurrent, reliable systems. For my org, building a distributed webapp, we chose it over the languages you listed because of how much you get "out of the box" with Elixir.

Saša Jurić's talk "The Soul of Erlang and Elixir" (https://www.youtube.com/watch?v=JvBT4XBdoUE) is a good introduction to why someone might choose Elixir. The payoff is the slide (https://imgur.com/gallery/G6lfUW6) where he compares the stack of a "traditional" web app (Nginx + Ruby on Rails + Go + Redis + Mongo + Cron + Upstart) to the Erlang rewrite of the same app, which is... just Erlang.

This isn't to say that Erlang ships a complete replacement for Redis, Mongo, Upstart, etc.—but it provides most of the functionality that most apps will need, such that your dependency tree can be much simpler. It's really nice to not have to become an expert in all the infrastructure surrounding a normal web app and instead just learn Erlang/Elixir.

[rkangel]

> It's really nice to not have to become an expert in all the infrastructure surrounding a normal web app and instead just learn Erlang/Elixir.

It is also so much easier to test when all of your architecture is in one form. You don't have to spin up whole deployments on real infrastructure to see if the parts still talk - your normal local unit testing architecture gets you much more confidence.

[jamil7]

I hadn't seen that slide, it's pretty compelling. Is there a story for typechecking or a typed language that runs on BEAM? This is one aspect that holds me back a little.

[s3cur3]

Erlang's type checker Dialyzer has an Elixir wrapper called Dialyxir (https://github.com/jeremyjh/dialyxir). As someone coming from C++, Dialyzer leaves a lot to be desired—I still miss C++ type checking—but it's better than nothing.

The Norm library (https://github.com/keathley/norm) is an attempt at higher-level, more expressive type checking which I think shows a lot of promise, but I've not adopted it in a real project yet.