Aha, thanks, this works great! Indeed, I was missing those two pieces, and there was also one other slight misconception I had to get past: it turns out that I implicitly thought 'stack build' meant 'do whatever is in the local stack.yaml', but I guess it actually means 'build the package in the working directory (using stack.yaml to guide how that should happen)'. So when I put 'packages: ' and tried to 'stack build' of course I got an error saying that it could not find a package. But once I figured out that I have to say 'stack build package1 package2 ...' it works great. Thanks again for the help --- and also thanks to Neil for the example.