I like your solution but that's kind of the rub about Go, at least at this stage of its still-early life. You have to re-invent the wheel a lot. It's frustrating to have to implement things that you know exist elsewhere, especially things like collections.defaultdict in Python.

Agree re: boilerplate. Much slimmer than Java or C++. And the build times, my God, the build times. It almost makes up for not having a true REPL.