You can see an example of this in this Nix setup I'm experimenting with. The problem is that psc doesn't provide any means for depending on code you've already compiled. If you want to use precompiled code, you have to copy it into the output directory, and include the sources for that code in the list of sources for psc. This is at best clumsy, and is prone to issues with timestamps changing on copy. It'd be nice if there were some intermediate representation (corefn?) that preserved the necessary information for compiling against.