1. Start it using ‘M-x ielm’.
   

   00:37

   
2. 345(#o531，#x159)
   

   01:22

   
3. （+ 5 5）elisp 运算符在前面
   

   03:14

   
4. (+ 5 5 10 20 30)
   

   03:14

   
5. (defun add-nums (a b) (+ a b))
   

   05:14

   
6. This code is called the function definition and is created by evaluating a Lisp expression that starts with the symbol defun (which is an abbreviation for define function).

(require 'ert) ERT: Emacs Lisp Regression Testing