[H2CO3]

Exactly, Sparkling uses reference counting, and one of the major TODOs is the introduction of weak references in order to address the issue of cycles.

[sdegutis]

Implementing weak references sounds like a feature that will make the language's source code much more complex than the simplicity emphasized in your goals.

[any1]

nim has some sort of automatic cycle detection. You might want to look into how they do it. It doesn't hurt to check it out.