Here is a simple program that creates an instance of the RegPolygon class, changes the length of a side, and displays the perimeter:

// Polygon.prg

// A simple program example

//

local poly

poly = new RegPolygon( )

poly.length = 4

? poly.perimeter( ) // Displays 12

class RegPolygon

this.sides = 3 // Default number of sides 

this.length = 1 // and default length 

function perimeter( ) 

return this.sides * this.length 

endclass