My interpretation is that the __typenames__ are merely there as placeholders so the program will compile, but fail at runtime during the tests. It's a tad odd, but the user is meant to replace the __typenames__ with their own values to make the tests pass. While doing so the user would be reading all of the code, and hopefully wind up grokking it.

It seems like a superficial tabs-versus-spaces kind of point, but when you see how the standard library is organized and how package names interact with actual programs, you grok why underscores make people wince; "foo_bar" should either be "foo/bar", or just plain "bar".

The import statement at the top of the file can clarify what the origin of a package is, but in the program body itself, the package name should make the library feel as natural as "fmt" or "io" or "math".