AppleScript: The Definitive Guide, 2nd Edition

Chapter 20. Dictionaries

In Part II you learned the AppleScript language. It's essential to know this language if you're going to write AppleScript code; yet, ironically, the AppleScript language on its own won't get you very far. That's because AppleScript, all by itself, doesn't do very much; its real power and purpose lies in communicating with scriptable applications, which provide powers that AppleScript lacks. In order that you, the AppleScript programmer, may harness its powers, a scriptable application extends the vocabulary of the AppleScript language. For example, AppleScript can't make a new folder on your hard drive, but the Finder can; therefore the Finder extends AppleScript's vocabulary, supplementing it with terms such as make and folder so that you can use AppleScript to command it (the Finder) to make a folder. This extended vocabulary is called a scriptable application's terminology . A dictionary is the means by which a scriptable application or scripting addition lets the world know how it extends AppleScript's vocabulary.

A dictionary has two audiences—AppleScript and the AppleScript programmer. Let's consider how each of these audiences uses a dictionary:

AppleScript

AppleScript uses an application's dictionary at compile time to look up the terms that the programmer uses. In this way, AppleScript confirms that the terms really exist; as they don't exist within AppleScript itself, AppleScript cannot know without a dictionary that the programmer isn't just ...