Apart from the obvious Jane Street example, quite a few. F# is used pretty widely at this point in the Chicago area. Many of the larger banks either have their

Apart from the obvious Jane Street example, quite a few. F# is used pretty widely at this point in the Chicago area. Many of the larger banks either have their own private dialect of ML or a strict, ML-like subset of Haskell (Standard Chartered). But for most it's not their primary language; those roles are usually still filled by C on the server and some GUI-friendly language for the trader apps. It's mainly used less latency-sensitive work that is more financial modeling in nature. Sorry for being vague with names; other than Jane Street and Standard Chartered, most of them will only talk about it confidentiality. Many take secrecy to the point of lunacy.