After storing then resetting some of our system variables we create a list of names that will appear in our list box. Following this we load our dialogue box, setting up error checking to make sure that the dialogue file is loaded before continuing. On it's own a DCL definition does nothing more than define a lifeless dialogue box. At that time the tile passes the string back to AutoLisp. AutoLisp then converts the string to functioning code and the code is executed.
Lets look at another code fragment.
It terminates the dialog box. It assigns a value of T to the variable userclick1. Now that everything is set and ready to go, we invoke the dialogue box. Once it is on the screen, it controls the programme flow, until the user hits OK, Cancel or double-clicks on an item in the list box. The user has made his selection so now we can unload the dialogue box.