The Principles of the Flix Programming Language.

We present the design values and design principles of the Flix programming language, a functional-first, imperative, and logic programming language. We explain how these values and principles came into being and how they have influenced the design of Flix over the last several years. The principles cover most facets of the Flix language and its ecosystem, including its syntax, semantics, static type and effect system, and standard library. We present each principle in detail, including its origin, rationale, and how it has shaped Flix. We believe that codifying a language's design values and principles can serve as a powerful medium for discussing and comparing programming language designs and we hope our presentation will inspire future language designers to document their languages' design values and principles.