Can an applescript be made to stop when in a repeat?

Question

Hi all,
Im very new to applescript but have made what seems to be a functioning applescript to save attachments from emails based on some examples I found through internet searches.  My current problem is that, once I have set it to run I cant quit it until it is finished.  Is there some script I am missing to make it quit?  I have tried:-
On quit
tell me to quit ---- or quit me  -- or various combinations
end quit
I think the issue is that the quit command gets 'lost' as the script is 'trapped' in a repeat loop until it finishes the task.  The only way I have found to stop it is through force quitting the application.
Below is my script for reference.
using terms from application "Mail"
          on perform mail action with messages theMsges
                    set FolderChoose to choose folder with prompt "Choose the folder"
                    repeat with ThisMessage in theMsges
                              set nameof to "DONTGO" --- variable to stop creating folders if an attachment does not exist
                              tell application "Mail"
                                        set Attached to mail attachments of ThisMessage
                                        repeat with ThisAttach in Attached
                                                  set nameof to name of ThisAttach
                                        end repeat
                              end tell
                              try
                                        set nameof2 to nameof
                              on error
                                        set nameof to "DONTGO"
                              end try
                              if not nameof is "DONTGO" then
                                        set Mesdate to date received of ThisMessage
                                        set {year:y, month:m, day:d} to Mesdate -- series of commands to get the date in the format I want to create the folder name
                                        set y to y as string
                                        set y to text 3 thru 4 of y
                                        set m to m as integer
                                        if d < 10 then set d to "0" & d as string
                                        if m < 10 then set m to "0" & m as string
                                        set filename to y & m & d as string
                                        try
                                                  tell application "Finder"
  make new folder at alias (FolderChoose as text) with properties {namefilename as text)}
                                                  end tell
                                        end try
                                        set newfolder to FolderChoose & filename & ":" as string
                                        tell application "Mail"
                                                  set Attached to mail attachments of ThisMessage
                                                  repeat with ThisAttach in Attached
                                                            try
                                                                      save ThisAttach in (newfolder as text) & (name of ThisAttach as text)
                                                            end try
                                                  end repeat
                                        end tell
                              end if
                    end repeat
          end perform mail action with messages
end using terms from
using terms from application "Mail"
          on run
                    tell application "Mail" to set sel to selection
                    tell me to perform mail action with messages (sel)
          end run
end using terms from

Answer 1

What you're asking is a little off the beaten track for applescript (applescript is not threaded, and is intended to run from beginning to end without interruption).  If you think it's worth the effort, you can fake it.  The easiest way I can think of, off hand, is to use a stay open application, and break up the code execution in the idle handler.  the pseudocode for that would be something like:
global listIndex, globalList
on run
          set listIndex to 1
          tell application "Mail"
                    set globalList to messages
          end tell
end run
on idle
          repeat with idx from listIndex to listIndex + 50
                    tell application "Mail"
                         -- process item idx
                    end tell
          end repeat
  -- advance index to start of next 50
          set listIndex to listIndex + 50
  -- idle for a tenth of a second, to give the application the opportunity to process any pending quit request
          return 0.1
end idle
it's not elegant, but it would work.  There might be other ways to accomplish it, but I'd have to think on that a bit.