AppleScript: The Definitive Guide

What’s in a Dictionary

This section describes the contents of a dictionary. This is primarily so that you can interpret a dictionary when you read it in an application such as the Script Editor.

Enumerations

An enumeration is a value that must be one of a fixed list of four-letter codes. These four-letter codes are called enumerators ; and the enumeration itself also has a four-letter code, identifying the entire set of its enumerators. Thus, by using the four-letter code of an enumeration, a dictionary can specify that a value must be one of the enumerators of that enumeration.

For example, BBEdit’s dictionary entry for the close command reads, in part:

close reference [saving yes/no/ask]

The triad of values yes/no/ask is an enumeration. The dictionary actually just says here that the saving parameter is a 'savo‘. That’s the four-letter code for an enumeration. The script editor application, presenting this information in human-readable form, has looked up the 'savo' enumeration in the dictionary and has fetched the English-like equivalents of its three enumerators. The four-letter code for the enumeration itself, 'savo', has no English-like equivalent.

By and large, an enumerator is the same thing as a constant, as discussed in Chapter 17. If you ask AppleScript for the class of yes, it tells you it’s a constant.

AppleScript uses this information to translate between English-like terms and four-letter codes, but the compiler does not check to see whether the value you actually supply ...