AppleScript to change case of clipboard text to uppercase or lowercase

Change Case of Clipboard.scpt

on changeCaseOfText(theText, theCaseToSwitchTo)
	if theCaseToSwitchTo contains "Lowercase" then
		set theComparisonCharacters to "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
		set theSourceCharacters to "abcdefghijklmnopqrstuvwxyz"
	else if theCaseToSwitchTo contains "Uppercase" then
		set theComparisonCharacters to "abcdefghijklmnopqrstuvwxyz"
		set theSourceCharacters to "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
	else
		return theText
	end if
	set theAlteredText to ""
	repeat with aCharacter in theText
		set theOffset to offset of aCharacter in theComparisonCharacters
		if theOffset is not 0 then
			set theAlteredText to (theAlteredText & character theOffset of theSourceCharacters) as string
		else
			set theAlteredText to (theAlteredText & aCharacter) as string
		end if
	end repeat
	return theAlteredText
end changeCaseOfText

set theDialogText to "Change case of clipboard text?"
set userResponse to the button returned of (display dialog theDialogText buttons {"Uppercase", "Lowercase"})
set theString to changeCaseOfText(the clipboard as text, userResponse)

set the clipboard to theString