Code Staging in GNU Guix

GNU Guix is a " functional " package manager that builds upon earlier work on Nix. Guix implements high-level abstractions such as packages and operating system services as domain-specic languages (DSLs) embedded in Scheme. It also implements build actions and operating system orchestration in Scheme. This leads to a multi-tier programming environment where embedded code snippets are staged for eventual execution. This paper presents G-expressions or " gexps ", the staging mechanism we devised for Guix. We explain our journey from traditional Lisp S-expressions to G-expressions, which augment the former with contextual information and ensure hygienic code staging. We discuss the implementation of gexps and report on our experience using them in a variety of operating system use cases-from package build processes to system services. Gexps provide a novel way to cover many aspects of OS connguration in a single, multi-tier language, while facilitating code reuse and code sharing .