Solution to Exercise 3.12

[jonathantorres]

• After the call to const z = append(x, y), tail(x) = ["b", null]. Since append creates a new copy of x with the elements of y.

• After the call to const w = append_mutator(x, y), tail(x) = ["b", ["c", ["d", null]]]. Since append_mutator sets the tail of the last pair of x to y.

[martin-henz]

The first picture is not correct, because the list

["c", ["d", null]]

is shared between y and z.