How to use dynamic variables as elements of an array

I would like to use an array or list to store dynamic variables for later retrieval via an index. So if I have:

(defparameter *foo* '(1 2 3))
(defparameter *bar* '(3 4 5))
(defparameter *baz*
  (make-array 2 :initial-contents '(*foo* *bar*)))

I would like to retrieve *foo* by calling (aref *baz* 0) and have this return '(1 2 3)

Of course, this doesn't work and the *foo* stored in *baz* isn't even the special variable I defined at top-level, as shown when I try to do (elt (aref *baz* 0) 1) which only returns an error and not the value 2. Let me say I am new to Common Lisp and I don't even know how to describe this question in a way that helped me in searching through CLHS, etc. Any help would be appreciated!

You need to understand the difference between a symbol (which is a data type in Lisp) and its value. The symbol exists as an object. The value of a symbol is either the result of an evaluation or can be retrieved by accessing the symbol value. Lisp is one of the few languages where a symbol is a first class datatype and which has also a value which can be set and bound.

> '*foo*
*foo*       ; the symbol *foo* itself

> *foo*
(1 2 3)     ; the value of the symbol *foo* -> this list

> (eval '*foo*)
(1 2 3)     ; the value of the symbol *foo* -> this list


> (symbol-value '*foo*)
(1 2 3)     ; the value of the symbol *foo* -> this list

One can retrieve the value of a symbol with the function symbol-value:

(symbol-value '*foo*)

(let ((symbol '*foo*))
  (symbol-value symbol))

I suggest you to read When to use ' (or quote) in Lisp? and CLHS quote entry for a comprehensive explanation.

I will just focus on two problems in your code:

Usage of quote

Look at '(*foo* *bar*). quote stops the evaluation of these two symbols, so result of this expression will be a list with two symbols, *foo* and *bar*.

Compare that with (list *foo* *bar*)- during evaluation, symbols *foo* and *bar* are evaluated to their values, so the result will be '((1 2 3) (3 4 5)).

Usage of quoted lists

As CLHS quote entry says:

> The consequences are undefined if literal objects (including quoted
> objects) are destructively modified.

If you want to modify your lists later, you should create them with list or another function.

So, your code should look like this:

(defparameter *foo* (list 1 2 3))
(defparameter *bar* (list 3 4 5))
(defparameter *baz*
  (make-array 2 :initial-contents (list *foo* *bar*)))

I would also consider using 2d array, so you can combine elt + aref into one (aref *baz* 0 0), but that depends on the exact problem you're trying to solve.