The final classify example has me really puzzled. I can't see the array creation, nor see what the test does.

I omitted the array creation, because it's the same as above (array of pairs)

The test does basically nothing, it just returns the Pair unchanged. Since it is supposed to return a Pair anyway, it nicely fits into what .classify attempts.

BTW, what do you mean by "diplomatic perl 6"

I meant to write 'idiomatic', made a typo, and picked the wrong suggestion from my spell checker :-)