I'm in the same boat as you.

Right now for the frontend we selected Elm.

Now for backend I've been playing with

Elixir and Haskell

Elixir has the nice syntax of ruby with all the performance of Erlang. So that makes it a good candidate however what I don't like about it is: - it isn't strongly typed... and once you get used to types and all the bugs it catches you can't go back. - although variables are inmutable they behave as if they look a lot like mutable state and I don't want to lose that warranty either.

Then there is Haskell. Haskell is great until you need to do IO. And 80% of the webdevelopment is IO... either to the database, to an API or HTML... and all the current options seem overly complicated. I tried haskell with Servant which gives strong type to an API but the syntax is ugly Used Scotty (like ruby's Sinatra) but then the URLs are strings and when definning APIs you can't specify the types. Then I tried with Yesod I don't like such heavy frameworks and try to avoid Template Hasell...

So I continue to search....

Next in my list consider is FSharp and OCaml

Very interesting! I've been using Elixir on a smaller project and have been quite impressed. It just feels friendly and palatable, while also being quite powerful for highly concurrent workloads.

Agreed on the typing, however.

Have you guys looked into Dialyzer?

Dialyzer is a static analysis tool for Erlang and other languages that compile to BEAM bytecode for the Erlang VM. It can analyze the BEAM files and provide warnings about problems in your code including type mismatches and other issues that are commonly detected by static language compilers. The analysis can be improved by inclusion of type hints (called specs) but it can be useful even without those. For more information I highly recommend the Success Typings paper that describes the theory behind the tool.

That's from the Dialyxir (for using Dialyzer w/Elixir) github page: https://github.com/jeremyjh/dialyxir

More: http://learnyousomeerlang.com/dialyzer

(Perhaps this should be read first: http://learnyousomeerlang.com/types-or-lack-thereof )

And this is the Success Types paper behind it (mentioned in the excerpt above):

https://www.it.uu.se/research/group/hipe/papers/succ_types.p...