NoRedInk[0] also uses some Haskell in their backend, as well as Elm for most of their frontend. They've also worked some with Roc according to a blog post from

NoRedInk[0] also uses some Haskell in their backend, as well as Elm for most of their frontend. They've also worked some with Roc according to a blog post from a few years back; not sure if using it. [0] https://blog.noredink.com https://blog.noredink.com