You won't believe what programming language this Wall Street firm uses

Joab Jackson

One Wall Street firm found computational success not on the traditional path of enterprise Java, but in an obscure functional programming language called Caml, which offered the perfect tradeoff of concision and readability.

Trading firm Jane Street says Caml has given it a powerful set of tools for building large programs that have to run quickly and without errors.

"A huge amount of day-to-day programming is case analysis. Getting your programs right is really hard, and any tool you can get from the system to help catch errors is helpful," said Yaron Minsky, head of the technology group at Jane Street, speaking Friday at the QCon developer conference in New York.

Jane Street is a proprietary trading firm that is the world's largest industrial user of Caml and OCaml, the object-oriented version of Caml.

All of Jane Street's trading and ancillary systems use Caml, with the exception of some C code for low-level system interfaces and some Visual Basic script powering analyst spreadsheets. All in all, Caml code handles about US$20 billion of trades every business day at Jane Street.

The company employs about 60 programmers who either knew Caml from their college days or were smart enough to be able to learn it during training. Another 90 or so non-programmers at the company use it as well.

Jane Street's use of Caml was almost accidental, Minsky said. Caml is a dialect of the ML functional programming language, which is widely used in universities as a way to teach programming but hasn't yet found widespread success outside academia.

Minsky started at Jane Street while still in graduate school a decade ago. Since he was familiar with Caml, he composed a number of experimental programs for the company that were later pressed into production. He got hired, too, as soon as he finished his Ph.D. in distributed systems.

At the time, Jane Street was "more trader-heavy than technology-heavy," Minsky said. There was a lot of VB code on spreadsheets, though this approach did not scale well for the company, given that there was no system for change management to update the code across all the user's computers.

As the company became more immersed in the world of computer trading, Minsky deployed Caml on what would become the company's core systems.

Jane Street also looked at Java, which many trading firms use, but the way enterprise Java programs are constructed, with their dynamic object-oriented approach, can make them difficult to understand and reason about, he said.

He noted that one analyst at the company likes to review any code that runs on the system, even though he is not a programmer. He just sits down and works through the code until he understands what is going on. Caml can be easy to understand, once you get the syntax down.

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