Option Explicit

Class cls_List
	Public Head
	Public Tail
End Class

Function fun_cons(head, tail)
	Dim list
	Set list = New cls_List
	list.Head = head
	Set list.Tail = tail
	Set fun_cons = list
End Function

Function fun_rev(list, rev)
	If list Is Nothing Then
		Set fun_rev = rev
	Else
		Set fun_rev = fun_rev(list.Tail, fun_cons(list.Head, rev))
	End If
End Function

Function fun_join(list, sep)
	If list Is Nothing Then
		fun_join = ""
	Else
		If list.Tail Is Nothing Then
			fun_join = list.Head
		Else
			fun_join = list.Head & sep & fun_join(list.Tail, sep)
		End If
	End If
End Function

Function fun_div(s, n)
	If Len(s) = "" Then
		Set fun_div = Nothing
	Else
		Dim list
		Set list = Nothing

		Dim i
		
		For i = 1 + n To Len(s) Step n
			Set list = fun_cons(Mid(s, i - n, n), list)
		Next
		
		Set list = fun_cons(Mid(s, i - n, Len(s) - (i - n) + 1), list)
		
		Set fun_div = fun_rev(list, Nothing)
	End If
End Function

Function fun_format(num, n, sep)
	Dim r
	r = StrReverse(num)
	Set r = fun_div(r, n)
	r = fun_join(r, sep)
	r = StrReverse(r)
	fun_format = r
End Function

Sub fun_main()
	Call WScript.Echo(fun_format("", 3, ","))
	Call WScript.Echo(fun_format("0", 3, ","))
	Call WScript.Echo(fun_format("90", 3, ","))
	Call WScript.Echo(fun_format("890", 3, ","))
	Call WScript.Echo(fun_format("7890", 3, ","))
	Call WScript.Echo(fun_format("67890", 3, ","))
	Call WScript.Echo(fun_format("567890", 3, ","))
	Call WScript.Echo(fun_format("4567890", 3, ","))
	Call WScript.Echo(fun_format("34567890", 3, ","))
	Call WScript.Echo(fun_format("234567890", 3, ","))
	Call WScript.Echo(fun_format("1234567890", 3, ","))
End Sub

fun_main