# Set the index-th element but wrap
	#
	# Whereas `self[]=` requires the index to exists, the `modulo` accessor automatically
	# wraps overbound and underbouds indexes.
	#
	# ~~~
	# var a = [10,20,30]
	# a.modulo(1) = 200
	# a.modulo(3) = 100
	# a.modulo(-1) = 300
	# a.modulo(-10) = 301
	# assert a == [100, 200, 301]
	# ~~~
	#
	# REQUIRE `not_empty`
	# ENSURE `self[modulo_index(index)] == value`
	fun modulo=(index: Int, value: E) do self[modulo_index(index)] = value