I think WhatsApp was Elixir Erlang, actually; and they're still using it -- here's a paper-abstract[0] from Sept.2022 (and video of a talk[1]) about their open

I think WhatsApp was Elixir Erlang, actually; and they're still using it -- here's a paper-abstract[0] from Sept.2022 (and video of a talk[1]) about their open-source "EqWAlizer" tool[2] for statically-typing Erlang (as-is). (EqWAlizer was discussed on an Erlang-related podcast[3], including its relationship to Dialyzer -- the original Erlang type-checking tool -- and it was briefly discussed on HN[4]). [0] https://dl.acm.org/doi/10.1145/3546186.3552537 https://dl.acm.org/doi/10.1145/3546186.3552537 [1] https://www.youtube.com/watch?v=do9f2FKsKxM https://www.youtube.com/watch?v=do9f2FKsKxM [2] https://github.com/WhatsApp/eqwalizer https://github.com/WhatsApp/eqwalizer [3] https://www.beamrad.io/35 https://www.beamrad.io/35 [4] https://news.ycombinator.com/item?id=32330284 https://news.ycombinator.com/item?id=32330284