pair(a, b)
Return a new pair whose head is the object a and whose tail is the object
b.
A pair can also be constructed by using the : operator as in, a:b.
The form a: will create the pair a:void. This form is useful for
specifying spliced indices into lists and arrays.
pair(3, 4)
// 3:4
pair(3, pair(4, 5))
// 3:4:5
pair(3, 4:(5:[]))
// [3, 4, 5]