Books are by default sequential, but they also offer a lot of different means of indexing to get what you want: the table of contents, the index, or just flipping through. And if you have no idea where you start, you know where to begin: at the beginning of the book. Software projects are often not linear, but trees where the leaves are files. Even in a reasonably modular code base, there's no real beginning. But I'd disagree that code is inherently unsequential when it comes to understanding it. One would have to do exactly as you suggest. They'd have to start with an overview, tell the conceptual story, then write the implementation. They'd have to write a literate program.