I/O access from code running on host computer?

Two ways you could approach this. One is to use a network socket to communicate between your Mac and the Beagle. Take a look at http://beej.us/guide/bgnet/ for some general info on sockets.

You also might be able to use an RPC to call from the Mac to the Beagle, though I’ve not tried this with a Mac or on the Beagle.