The switch statement determines if the point is on the green diagonal line where x == y, on
the purple diagonal line where x == -y, or neither.
The three switch cases declare placeholder constants x and y, which temporarily take on
the two tuple values from point. These constants are used as part of a where clause, to
create a dynamic filter. The switch case matches the current value of point only if the where
clause’s condition evaluates to true for that value.
As in the previous example, the final case matches all possible remaining values, and so
a default case is not needed to make the switch statement exhaustive.