REALBasic: TDG, 2nd Edition

Chapter 31.  Interapplication Communications

The Macintosh’s system-level mechanism for letting applications communicate with one another is Apple events .^[154] An application that defines a repertoire of Apple events to which it is prepared to respond is described as scriptable . Another application can send to a scriptable application an Apple event from the scriptable application’s defined repertoire, to give it a command or to ask for information.

An Apple event is an ingeniously designed package of data, and can express a command or query of astonishing power and complexity. This means, however, that an Apple event is itself a particularly complex data structure. A convenient way to construct and send Apple events without having to deal with the details of their raw structure is through AppleScript , a programming language that encodes Apple events as English-like expressions. This, too, is a system-level mechanism; AppleScript code is interpreted and executed as Apple events by way of the system’s Open Scripting Architecture, or OSA. (The term “AppleScript” properly refers to the language, but I use it also to refer to a script—a self-contained piece of executable code written in that language—so as not to have to talk about an “AppleScript script.”)

REALbasic can construct and send raw Apple events. Also, it can incorporate and execute AppleScripts written and compiled in some other milieu, such as Apple’s own Script Editor. Through both these means, ...