It's possible to satisfy a set of requirements with code that's low quality. There's the maintainability of the code, for example, or the performance of the system.
It's meant as an example. The function receives something, which we call v, and returns something else, which we call e. It's not meant to be taken literally as the variable names - otherwise, you are right, e is undefined in that example.
He is just showing how the syntax of a Scheme function corresponds to the structure of a JavaScript function.
It’s academic and comprehensive, that’s the issue. It’s not about writing a production grade compiler, though, in my humble opinion. There are more things to learn for that, unfortunately… is just a pretty big topic with lots of stuff to learn.
'Engineering a Compiler' by Cooper & Torczon is a great resource. It gives context on each topic, explains them clearly, and at the same time, I think, it is a really good resource from an academic point of view. It still requires some investment in terms of time and effort, but I found it more approachable than the Dragon book. I would say that both cover more or less the same introductory stage to compilers construction. If you have read the Dragon book, I have the feeling that you are perfectly well prepared to write your own compiler.
