My point is mainly that the package specification in Guix is very verbose -- I must hack (and in some cases generate) package files to do what I want to do. Th

My point is mainly that the package specification in Guix is very verbose -- I must hack (and in some cases generate) package files to do what I want to do. The approaches you mention for generating package variants seem to generate new packages -- how do you deal with the profusion of packages that result here? Don't get me wrong -- Nix is the inspiration for a lot of what Spack is doing, but we've added to it by making an attempt to template the packages by version, compiler, and options. So the usr don't have to "create" the package variant at all: they just `spack install numpy %intel@15.0.1` to compile with the Intel compiler, because the compiler can be swapped in/out of any build. We do similar things with versioned interfaces like MPI -- you can swap OpenMPI or MVAPICH in/out of a build. I have not seen anything to lead me to believe Guix allows this in a simple way, without generating a new package and copying a lot of boilerplate from the old one. The graph transformation stuff you mentioned in your other comment is promising, though.