jane-street-functional-trading
Jane Street Style Guide
Overview
Jane Street is a quantitative trading firm and market maker that trades ~$17 billion daily across equities, bonds, options, and ETFs. Famous for using OCaml (a functional programming language) for nearly all trading infrastructure, they prioritize correctness, expressiveness, and the ability to reason about code.
Core Philosophy
"We use OCaml because when you're trading billions of dollars, you want to be able to reason about your code."
"The type system is your first line of defense. If it compiles, it's probably correct."
"Make illegal states unrepresentable."
Jane Street believes that in high-stakes systems, the cost of bugs is astronomical. Functional programming, strong typing, and immutability dramatically reduce error rates compared to imperative approaches.
Design Principles
- Correctness by Construction: Design types so invalid states cannot be represented.