Tommy Teague supplied a great example of combined parameter input with repeated AutoCAD commands in his Cut Window (Tip#1963) utility. This handy function lets you cut and trim objects inside a closed boundary by repeating the Trim command. Load the LSP file and type in CA or Cleararea to activate the command. Select a series of boundary objects and an inside point-the rest is automatic.

This clever routine leverages the AutoCAD commands inside AutoLISP and lets you open up a window for placing other graphics or text. Note that objects you want to trim out of the enclosed area must be the kind that can be trimmed.