The GNU Guix project invented G-Expressions to make it easier to "stage" data or code, in the form of S-Expressions, for later manipulation or evaluation. They are similar to S-Expressions, hence the name, but they provide useful code staging features beyond what can be easily accomplished with just "quasiquote" and "unquote". A high-level object (such as a Guix package) can be included in a G-Expression; the transitive dependencies of that high-level object will then be automatically carried along with the G-Expression. When the G-Expression is converted to an S-Expression and stored on disk for later manipulation or evaluation, the high-level object will be automatically "lowered" to an appropriate representation (such as the package's output path) via a "compiler". Compared to direct manipulation of S-Expressions, G-Expressions can provide a simpler and more intuitive way to stage data or code.

The Guix project uses G-Expressions to accomplish a wide variety of tasks, including:

• Building the latest version of Guix via "guix pull"
• Executing the "liberation" procedure to convert Mozilla Firefox's source code into GNU IceCat's source code
• Building Docker containers from scratch
• Executing activation actions during system boot
• ...and more!