Evaluation

A key to understanding any Lisp is grasping the idea of how expressions should be evaluated. Roughly, the steps are:

1. Reader: Code as a string becomes a sexp, either an atom or an expression. Later, we'll discuss that there are forms that users can input, but they look different until processed by the reader into a proper sexp. It will be explicitly mentioned in this book if that's the case. Until then, our string inputs will match the string representation of a resulting sexp.
2. Macro expansion: Some sexps may become other sexps.
3. Eval: The final sexp is evaluated.

In subsequent chapters, we'll demystify all of it. For now, steps 1 and 2 will be transparent.