We present Flix, a declarative programming language for specifying and solving least fixed point problems, particularly static program analyses. Flix is inspired by Datalog and extends it with lattices and monotone functions. Using Flix, implementors of static analyses can express a broader range of analyses than is currently possible in pure Datalog, while retaining its familiar rule-based syntax.

We define a model-theoretic semantics of Flix as a natural extension of the Datalog semantics. This semantics captures the meaning of Flix programs without imposing any specific evaluation strategy, allowing for different Flix solvers. We have implemented a prototype compiler frontend and runtime for Flix, and used it to express several well-known static analyses, including the IFDS and IDE algorithms. The declarative nature of Flix clearly exposes the strong connections between these two algorithms.