? def empty := []
# value: []

? def numbers := [1,2,3,4,5]
# value: [1, 2, 3, 4, 5]

? numbers.with(6)
# value: [1, 2, 3, 4, 5, 6]

? numbers + [4,3,2,1]
# value: [1, 2, 3, 4, 5, 4, 3, 2, 1]