nthFields(？)区切りでN番目の要素を取り出す

on nthFields(myStr, sep, num)
	set OriginalDelimiters to AppleScript's text item delimiters
	set AppleScript's text item delimiters to {sep}
	set myStr to text items of myStr
	set AppleScript's text item delimiters to OriginalDelimiters
	return item num of myStr
end nthFields

myStrをsep区切りでnum番目の項目を返す