OCaml

Typed functional programming without the ceremony. OCaml gives you Haskell-grade type inference and pattern matching but evaluates eagerly and lets you mutate when you truly need to, so performance is predictable and programs read like ordinary code. Since OCaml 5 its runtime supports shared-memory parallelism and effect handlers, closing its oldest gap. It is not an academic curiosity: Jane Street runs its trading systems on it, and Bloomberg and Docker appear among its industrial users. Real World OCaml, written by Jane Street's Yaron Minsky and Anil Madhavapeddy, is free to read online and is the book to pair with it. Expect some friction choosing between standard libraries and build setups at first.