# AutoLISP Evaluates every Expression

The LISP part of AutoLISP stands for *list processing, *which describes what happens when you run a routine: AutoLISP processes lists or, as we say here, evaluates expressions. If you type in an AutoLISP expression at the Command line it will return the results of the processed list.

*Command: (+ 18 6)
*24 Expression

*results*

- Each AutoLISP expression is enclosed in parentheses.
- Expressions are made up of a
*function*followed by*arguments*. The function is analogous to the “verb” or action of the expression, while the arguments are like the “nouns” or things that are acted upon.

- AutoLISP expressions are evaluated from left to right.
**Example: Basic Math Functions**

**Example: Basic Math Functions**

- An AutoLISP expression may have multiple arguments.

*Command: (+ 3 8 16 12 2)*

41

**Command: (- 60 15 12)
33**

- An AutoLISP expression can contain other AutoLISP expressions. Such
*nested*expressions are evaluated from the innermost parentheses outward.

*Command: (+ 3 8 (* 2 3))*

17

- Spaces are used to separate the different parts of an AutoLISP expression. Either a single space or multiple spaces, including tabs and carriage returns (the <enter> key), may be used. Spacing makes the expression more readable.

*Command: (+ 6 3)
9
*

*Command:*

**(+ 6**

(_>**3)**

9Note that in the last example, since we did not close our initial parentheses before hitting the <enter> key, AutoCAD returned with a different prompt “(_>” telling us that our AutoLISP expression is not complete and requires one more closing parenthesis.

**PRACTICE**

*Try out the following basic calculations. Estimated time for completion: 5 minutes.*

(**+ **8 4)

(**– **7 3)

(*** **5 2)

(**/ **10 5)

(**+ **10 17 21)

(*** **3 12 (**– **17 5))

(**+ **15 5 (*** **6 4))

(**/ **(**+ **6 3) (**– **18 15))

**Higher Math Functions**

AutoLISP is a math wizard. It can handle not only basic math functions but also anything that a good scientific calculator can do.

*Practice*

*Try out the following expressions. Estimated time for completion: 5 minutes.*

(abs 3.0)

(abs -3.0)

(sqrt 9)

(sqrt 9.0)

(min -3 7 6.0 10 0)

(max -3 7 6.0 10 0)

(sin (/ PI 2))

(1+ 3) (1- 3)