See the list of donors to the Haskell Foundation (at the bottom of https://haskell.foundation/ https://haskell.foundation/) and the testimonials on https://www.

See the list of donors to the Haskell Foundation (at the bottom of https://haskell.foundation/ https://haskell.foundation/) and the testimonials on https://www.haskell.org/ https://www.haskell.org/ for a subset of those firms who are using Haskell in production.