AppleScript: The Definitive Guide, 2nd Edition

Blocks

A block is one or more lines of code demarcated from its surroundings as having a separate nature or purpose. A block is announced by a line stating what type of block it is; then comes the code of the block; and finally the block is terminated by a line starting with the keyword end. Blocks can occur within blocks.

It's very easy to spot a block in AppleScript code, because in decompiled code its lines are indented from the announcement line and the termination line. For example:

myHandler( )
on myHandler( )
    repeat 3 times
        display dialog "Howdy"
    end repeat
end myHandler

That code contains two blocks. One is announced with the on myHandler line, and is terminated by the end myHandler line; everything in between them is the code of that block. That code consists of another block, announced with the repeat line and terminated by the end repeat line; the line of code in between them is the code of that block.

In this book I frequently refer to such blocks by their announcement keyword; for example, I might say "a repeat block."

Some blocks (just two, actually—tell blocks and if blocks) have single-line variants. This permits some rather twisted condensed syntax. For example:

tell application "Finder"
    if exists folder "Mannie" then
        reveal folder "Mannie"
    end if
end tell

You can reduce one or both of those blocks to a single line. So, this is legal (but I never talk this way, and I don't recommend you do either):

tell application "Finder" to if exists folder "Mannie" then reveal folder ...