>>> sum [] 0
>>> sum [42] 42
>>> sum [1..10] 55
>>> sum [4.1, 2.0, 1.7] 7.8
>>> sum [1..] * Hangs forever *
>>> sum [] 0 >>> sum [42] 42 >>> sum [1..10] 55 >>> sum [4.1, 2.0, 1.7] 7.8 >>> sum [1..] * Hangs forever *