Beginning Lua Programming

Chapter 9. Handling Events Naturally with Coroutines

When you're implementing an application, you, as a developer, should strive for simplicity and generality. These qualities make a program easy to extend and maintain, and allow it to be reused under a variety of platforms and circumstances. However, real-world requirements often conspire to make these objectives hard to attain. In this chapter, you'll learn how Lua coroutines provide you with an elegant and powerful tool that can dramatically simplify certain kinds of problems. For example, you can use coroutines to manage concurrent tasks, such as updating a progress bar and responding appropriately to user input while transferring a file.

You also use coroutines to provide contextual continuity to functions. A routine that is called intermittently as part of a continuing task may need to go to great lengths to reestablish the context of the task—that is, to remember "where it left off." For example, a tokenizing routine may be called from various parts of a parsing application yet must, when it is invoked, pick up right where it left off and return the next available token to the caller.

The event-driven nature of interactive programs can lead to logical discontinuities in the application source code. For example, in the interest of clarity, a program should invoke a window and wait until it is closed in much the same way that it calls a file reading routine. This way, directly after the call to show a window, the program can ...