OCaml doesn’t give a specific advantage in trading, it’s just that Jane Street like to be pretentious about most things including programming languages.
Do you mean no specific advantage relative to C++? If so, then wouldn’t it be an advantage that the GC lets you be (nearly) certain that you have no memory bugs?
For us, there were a couple advantages. For context, I work at FOSSA (https://fossa.com/). Our core product solves software supply chain needs in enterprises (around licensing and security), and our core technology is around compiler, build, and source code analysis.
Off the top of my head, 3 advantages stood out:
1. First, if you're not going that far off the beaten low-level path, Haskell has incredible productivity benefits. Effect tracking has enormous benefits for testability and understandability. If you've ever been down a debugging rabbit hole shaped like "there's no way this logging call is sending that API request", then you might be pleasantly surprised to discover that you can statically guarantee that this doesn't occur in Haskell programs! Pattern matching, algebraic data types (sum types!), and typeclass derivation make it much easier to make it impossible to construct invalid representations of data. Other languages are finally picking this up, but their versions of pattern matching often have caveats for backwards-idiom-compatibility. And monads are a very powerful abstraction. It's like being able to write your own semantics for async-await (I've talked more about this before at https://lobste.rs/s/7cllte/monads_part_six_really_what_is_mo...).
2. Haskell was a good domain fit for us. One thing we build is the FOSSA CLI (https://github.com/fossas/fossa-cli/), which runs in customer CI pipelines to analyze their builds. It's a very compiler-shaped problem: shell out to some tools, do a lot of parsing, think very hard, and then spit out a JSON blob to send back to the API. Our first version of this was written in Go. At the time of development, writing correct, testable parsers in Go was like pulling teeth. We have a relatively small headcount-to-product-surface-area ratio, and our team was running up against the overhead of rewriting traverse in Go over and over again (that's a Haskell-flavored joke, but if you've ever been annoyed at writing yet another for-loop in Go, you get it). We decided to hack out a prototype in Haskell, and it turned out to be a good fit.
3. Lastly, the kind of people who wind up working at FOSSA and are interested in the code analysis bits tend to be the same kind of nerds who love Haskell. We had lots of people on our team who were chomping at the bit to try it, so we decided to try it out. I really can't understate how big of a productivity difference it makes when people are working with tools that they actually enjoy rather than are merely forcing themselves to use. It is night and day.
