[TimmyMustGo]

I believe the "bottom part" should be interchangeable, like switching to a different CPU architecture, or switching to a different framework. The bottom part is an implementation detail. The API is important since that's what you interact with.

I think it's best to have as few dependencies as possible, try to keep everything independent and interchangeable. I like to view my code as a graph structure, try to keep the functions and its dependent functions as a Directed-Acyclic-Graph and avoid cycles.

[jlg23]

Beware, he was using the term "bottom up" in a meaning that diverges from current mainstream usage of the term: the bottom is the language, not the architecture.