the listboxes programming help system receiving the help command the first case chain or tree kinds of requests consequences of the chain of responsibility programs on github the command pattern when to use the command pattern command objects keyboard example calling the command objects building command objects the command pattern consequences of the command pattern providing the undo function creating the red and blue buttons undoing the lines summary references programs on github the interpreter pattern when to use an interpreter where the pattern can be helpful simple report example interpreting the language how parsing works sorting using attrgetter( the print verb the console interface the user interface consequences of the interpreter pattern programs on github xv