Post By: Hanan Mannan
Contact Number: Pak (+92)-321-59-95-634
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LISP - Constants

In LISP, constants are variables that never change their values during program execution. Constants are declared using the defconstant construct.

Example

The following example shows declaring a global constant PI and later using this value inside a function named area-circle that calculates the area of a circle.

The defun construct is used for defining a function, we will look into it in the 'Functions' chapter.

Create a new source code file named main.lisp and type the following code in it:

(defconstant PI 3.141592)
(defun area-circle(rad)
  (terpri)
  (format t "Radius: ~5f" rad)
  (format t "~%Area: ~10f" (* PI rad rad)))
  (area-circle 10)

When you click the Execute button, or type Ctrl+E, LISP executes it immediately and the result returned is:

Radius:  10.0
Area:   314.1592