LISP | Lisp interpreter in less than 500 lines

I made a lisp code that transforms a list of numbers into a tree. The rules of the tree are that the value of the left child node should always be smaller than the value of its parent node and the value of the right child node should always be higher than the value of its parent node.

Here is my lisp code:

I'm using SBCL 2.0.1.debian and Paul Graham's ANSI Common Lisp to learn Lisp.

Right in Chapter 2 though, I'm realizing that I cannot use setf like the author can! A little googling and I learn that I must use defvar or defparameter to 'introduce' my globals before I can set them with setq!

Is there any way to avoid having to introduce globals via the defvar or defparameter, either from inside SBCL or from outside via switches? Do other Lisp's too mandate this?

I understand their value-add in large codebases but right now I'm just learning by writing smallish programs, and so am finding them cumbersome. I'm used to using globals in other languages, so don't necessarily mind global- / local-variable bugs.

I am reading the book Object Oriented Programming in Common Lisp from Sonja Keene.

In chapter 2, the author says:

The procedure for determining which methods to call and then calling them is called generic dispatch. It happens automatically whenever a generic function is called.

This reminds me of the Dynamic Dispatch definition which is (according to Wikipedia):

Dynamic dispatch is the process of selecting which implementation of a polymorphic operation to call at run time. It is commonly employed in, and considered a prime characteristic of, object-oriented programming languages and systems.

Unfortunately, the wikipedia does not have an entry about generic dispatch.

Thus, I would like ask:

1 - Are dynamic dispatch and generic dispatch basically the same thing? What are the similarities?

2 - And what are the differences? Is dynamic dispatch some sort of subset of generic dispatch due to the flexibility of CLOS?

I need help to understand my code theoretically. Here is my lisp program:

I am trying to learn Common Lisp with the book Common Lisp: A gentle introduction to Symbolic Computation. In addition, I am using SBCL, Emacs, and Slime.

By the end of chapter 10, on the advanced section there is this question:

10.9. Write a destructive function CHOP that shortens any non-NIL list to a list of one element. (CHOP '(FEE FIE FOE FUM)) should return (FEE).

This is the answer-sheet solution:

I am trying to learn Common Lisp with the book Common Lisp: A gentle introduction to Symbolic Computation. In addition, I am using SBCL, Emacs, and Slime.

By the end of chapter 10, the author discuss the useful break function. In order to provide a background context, he presents this problematic function:

I'm trying to figure out how to parse S-expressions in C on my own, in order to store data and code for my own rudimentary Lisp (written as a learning exercise, not for production).

Before explaining my code and my reasoning, I should explain that all I know about S-expressions is the introductory section of the Wikipedia article on it, and the occasional glance at Common Lisp code, so the naming of my structs and variables may be a bit off.

My language of implementation is C, and before I defined any functions I created the following structs:

I'm running into an odd issue with Common Lisp's format directive that only shows itself in GNU CLISP, which leads me to wonder if it's a bug in the implementation.

Consider the following code

I am trying to learn Common Lisp with the book Common Lisp: A gentle introduction to Symbolic Computation. In addition, I am using SBCL, Emacs, and Slime.

By the end of chapter 9, the author shows the dribble tool. He shows the following:

I tried to reproduce the commands presented by the author. Considering the inputs, the only difference was the fact that I put a different location to save the file. In my environment, I did: