Here is one of the expressions from line 5 of the sample program in Lesson 1. The expression is a list, that is, it begins with an opening parenthesis and ends with a closing parenthesis. Every AutoLISP expression is a list. Functions are always placed at the beginning of the list. The function can also be called the operator, and the arguments can be called the operands.
Most functions have one or more arguments, but some functions have no arguments.
The AutoLISP interpreter Based on the above syntax, the AutoLISP interpreter has a relatively easy job whenever an expression is sent to it. Expressions are sent to the AutoLISP interpreter in several ways. One way is to type the expression at the AutoCAD command prompt. Other ways to send expressions to the AutoLISP interpreter include loading files that contain AutoLISP expressions and selecting menu items that include AutoLISP expressions. These methods are discussed in later lessons.