In Spack this would look like: spack install guis ^guile@<new version> How do you handle optional dependencies in this model? Or, a more complex case, de

In Spack this would look like: spack install guis ^guile@<new version> How do you handle optional dependencies in this model? Or, a more complex case, dependencies that are only present for certain versions of the package? Look at the gcc package in Spack: https://github.com/LLNL/spack/blob/develop/var/spack/repos/builtin/packages/gcc/package.py#L54 This builds gcc 4.x and 5.x versions, and it's pretty concise. The `mpc` and `isl` dependencies are only present when the version of gcc is 4.5 or higher, or 5.0 or higher, respectively. There's an iterative DAG-building step called concretization that looks at these types of constraints and tries to solve for a satisfactory DAG, which is then built in a functional style. I don't see how I would model that in Guix, and but in Spack it's a few lines, and there's command-line syntax to customize versions on the command line, not just programmatically. e.g.: spack install gcc@5.0 ^isl@0.11.1 ^mpc@1.0.2