Fix some things on an experimental future feature.
Still dirty code ofc, it will take a long to be adopted, but new
developers can watch the backstage's step-by-step test-driven solutions.
Former-commit-id: 739260b8662bff7164ba75ef36c81a6b564d53cc
Ok we did convert a regular `func([]string) func(string)bool` to
`func(anything...) func(string)bool`
Former-commit-id: 1097e5d61663f1b14867e807ae53e2ccbb6401a8