I use Haskell professionally in the area of quantitative finance in a large team with a multi-million line codebase. Everything is built upon domain specific libraries, sometimes many layers deep. And these libraries are constantly changing to keep pace with the business. Strong types tell us early when things are broken. Others are attempting to use Python for similar projects, but it isn't fun (we have some of their alumni).
Haskell's effect typing also helps us. For example, for reproducible calculations, it is critical that no data is pulled-in via a backdoor (i.e. a side effect). Even reading and using the current system datetime is something we want to prevent. This can be expressed in the types using Haskell.
So, highly reliable and completely transparent data processing. Awesome. Very interesting to know. I always assumed financial data processing, HFT, etc are done in java / C# or other mainstream languages.
And yes, in such a situation, Python will not be an easy fit.
Thanks a lot for sharing the info. Have been wanting to learn functional programming for a long time now. Specifically, I am planning to build computation systems based on Haskell, Scala, etc which sit behind a Message Queue server. Just to isolate the computation part from other mundane activities like HTTP request processing.
Haskell's effect typing also helps us. For example, for reproducible calculations, it is critical that no data is pulled-in via a backdoor (i.e. a side effect). Even reading and using the current system datetime is something we want to prevent. This can be expressed in the types using Haskell.