Extends existed module?

[simonls]

I think a single collection package would work too, if you use syntax as collection and then just have a file a.rkt in that package.

Single/Multi-Collection is orthogonal to Single/Multi-Package, this comment goes into more detail:

How to Organize Your Racket Library [blog]

I like your post a lot, I think starting out with racket it would have helped me to get up to speed in understanding that package organization strategy. The only thing I would like to state explicitly — because I am unsure that it is conveyed 100% to the reader — is that single-collection vs multi-collection is orthogonal to single-package vs multi-package. You can use them in any combination you like, e.g. in my define-attributes package I use single-collection with multiple-package. Sometime…