It's very hard to know exactly how much of WhatsApp uses Erlang (there is hardly any documentation of that besides vague public release docs), and at the end of

It's very hard to know exactly how much of WhatsApp uses Erlang (there is hardly any documentation of that besides vague public release docs), and at the end of the day, like I said, just because a system is written with a technology doesn't mean it was the best idea. > But Erlang has the concept of fail-fast and fault tolerance that make the lack of type safety not as big of a deal as it normally would be. That "fail fast" / "let it crash" thing that Erlang brags about has never been convincing to me. First, because you still need to implement all these supervisors yourself anyway so the complexity is still there. Second, it's an admission that because of its lack of static typing, Erlang developers are just throwing their hands in the air and try to make pass what is a fundamental flaw in the language (that you can't effectively and exhaustively catch errors) as a strength. Besides, Erlang doesn't have the monopoly on "let it crash": plenty of languages have better ways to catch and recover from errors, either through exceptions or algebraic data types that allow the compiler to make sure you have covered all the error cases.