content: on callback for arg
      -- Returns a string like "arc has 3 letters"
      arg & " has " & (count arg) & " letters"
  end callback
  
  set alist to {"arc", "be", "circle"}
  repeat with aref in alist
      -- Passes a reference to some item in alist
      -- to callback, then speaks the return value.
      say (callback for aref)
  end repeat
  