AppleScript: The Definitive Guide, 2nd Edition

Looping

The other major form of choice is looping , which involves branching back to the start of a block repeatedly. In AppleScript, looping is performed with repeat. There are several varieties of repeat, but repeat blocks all take same basic form:

repeat whatKindOfRepeat
    -- what to do
end repeat

Tip

Loops involve repetition—perhaps a lot of repetition. Therefore, although I'm no great believer in worrying too much about optimization, if you're going to optimize your code anywhere, loops are the place to do it. A small increase in speed can add up tremendously over multiple repetitions. See Chapter 22.

The big question with a repeat block is how you're going to get out of it. Obviously you don't want to repeat the repeat block forever , because that would be an infinite loop and would cause the computer to hang. Most kinds of repeat block include some instruction (as symbolized by whatKindOfRepeat in the syntax template), such as a condition to be evaluated, as a way of deciding whether to loop again.

There are also some special commands for hustling things along by leaping completely out of the repeat block from inside it. These are the premature terminations of a repeat block. They can be used with any form of repeat block. Here they are:

exit repeat

This statement exits the innermost repeat block in which it occurs. Execution resumes after the end repeat line.

try block

If the repeat block is inside a try block, throwing an error exits the repeat block by virtue of the fact that ...