Interrupting and resuming the "Building" phase?

I'm trying to do `sudo port install ghc` on my old PowerBook and it's taking longer than I can leave the laptop sitting around to do it. I tried hitting Ctl-C and then running the same command again (this always worked when fink, which I recently switched from, was building from source packages) but I just get an insurmountable error (as far as I can tell) and have to start over again. I know that normally make-driven builds can be interrupted and resumed, but I'm new to MacPorts. How can I do this? Thanks, Adam