What is lisp?

(defun average (b &rest a )
  (loop for i in a
        do (print i)))
(average 1 1 1 1 4)

What is a lisp image?

A lisp image is a collection of all of the information that the lisp compiler/interpreter needs to run a program

Lisp macros

Macros are a way to add additional syntax to the lisp language.

Consider the case where we want to set one value to multiple variables.

I'll write two macros to do this for me, one using a loop, and another using mapcar (maps function to each member of the list).

mapcar is definitly the more lispy way to do it, but I feel the loop way allows for more clarity in what is going on.

(defmacro setq* (value &rest variables)
  `(progn ,@(mapcar (lambda (x) (list 'setq x value)) variables)))
(defmacro setq-* (value &rest variables)
  `(progn ,@(loop for variable in variables
                  collect (list 'setq variable value))))
(setq-* "hi" x y z)

Essentially, we are creating a list of lists, or a list of statements. The ,@ sytax essentially just unwraps the outer list, leaving a sequence of evaluate-able statements.

(setq-* "hi" x y z)
;; this turns into
'((setq x "hi") (setq y "hi" ) (setq x "hi"))
;; which turns into (because of ,@)
(progn (setq x "hi") (setq y "hi" ) (setq x "hi"))
;; neat!