Section: Research Program

F*: A Higher-Order Effectful Language Designed for Program Verification

F*  [60] is a verification system for ML programs developed collaboratively by Inria and Microsoft Research. ML types are extended with logical predicates that can conveniently express precise specifications for programs (pre- and post- conditions of functions as well as stateful invariants), including functional correctness and security properties. The F* typechecker implements a weakest-precondition calculus to produce first-order logic formulas that are automatically discharged using the Z3 SMT solver. The original F* implementation has been successfully used to verify nearly 50,000 lines of code, including cryptographic protocol implementations, web browser extensions, cloudhosted web applications, and key parts of the F* typechecker and compiler (itself written in F*). F* has also been used for formalizing the semantics of other languages, including JavaScript and a compiler from a subset of F* to JavaScript, and TS*, a secure subset of TypeScript. Programs verified with F* can be extracted to F#, OCaml, C, and JavaScript and then efficiently executed and integrated into larger code bases.

The latest version of F* is written entirely in F*, and bootstraps in OCaml and F#. It is open source and under active development on GitHub. A detailed description of this new F* version is available in a POPL 2016 paper  [62] and a POPL 2017 one [22]. We continue to evolve and develop F* and we use it to develop large case studies of verified cryptographic applications, such as miTLS.