[grumdan]

As in, there are a handful of large projects the languages are used for. For Haskell, Facebook's spam detection system, Sigma[1], comes to mind, along with some use by banks (Standard Chartered); then there's a bunch of smaller places using Haskell (Wire, a secure messaging app, like Signal; Galois, a US defense contractor doing software verification and related things) plus some open-source tools like pandoc.

I know less about OCaml, but at least Jane Street is using it.

It's somewhat niche, but it's not like it's only used for hobby or toy applications.

[1] https://code.fb.com/security/fighting-spam-with-haskell/

[floatboth]

Facebook's static analyzer Infer https://fbinfer.com is written in OCaml.

There's a lot of OCaml in the program verification space: https://frama-c.com http://why3.lri.fr https://alt-ergo.ocamlpro.com

And for mysterious reasons, OCaml is now kinda popular for.. web frontends. Bloomberg created an OCaml-to-JS compiler https://bucklescript.github.io and Facebook (again!) created an alternative syntax https://reasonml.github.io and this combination is apparently a new hipster way of writing web apps.