rf: fix example program to build

[prattmic]

This way we can use this program to try out the examples later in the
docs.

[prattmic]

Would it be valuable to put a copy of this in testdata with a trivial command (mv F Func) to make sure it keeps working. Unfortunately that would just be copy, so it could easily get out-of-date.

[mdempsky]

Would it be valuable to put a copy of this in testdata with a trivial command (mv F Func) to make sure it keeps working. Unfortunately that would just be copy, so it could easily get out-of-date.

I think if we had a way to make sure they stay in sync, that would be worthwhile. But otherwise, I'd worry they fall out of sync, and then it doesn't add any value.

I'm not that concerned about it, but patches welcome. :)

[prattmic]

I've rebased for the build check update.

Sounds like we can just leave the testing as-is for now.