> If they're using a dynamically typed language to do monetary calculations, it's not going to be ideal.

I think this is an inaccurate take. No one in finance is doing accounting or model estimation using Python's floats; they are using numpy's float32 (or float64) type instead. I think a more accurate version of what you're saying is that static type checking is useful when modeling complicated contracts; this might be true, but I think it's not that important, as those things aren't that liquid anyway.

Jane Street's decision to use OCaml is almost as much about hiring and history as it is about language features.