GNU Guix functional package manager

 Guix is an advanced distribution of the GNU operating system
 developed by the GNU Project—which respects the freedom of computer
 users.
 .
 Guix supports transactional upgrades and roll-backs, unprivileged
 package management, and more. When used as a standalone distribution,
 Guix supports declarative system configuration for transparent and
 reproducible operating systems.
 .
 It provides Guile Scheme APIs, including high-level embedded
 domain-specific languages (EDSLs) to define packages and whole-system
 configurations.