unless evaluates the then branch if its condition is falsey, and evaluates the
else branch, if there’s any, otherwise. That is, it behaves in the opposite way of an
unless some_condition then_expression else else_expression end # The above is the same as: if some_condition else_expression else then_expression end # Can also be written as a suffix close_door unless door_closed?
To the extent possible under law, the persons who contributed to this workhave waived
all copyright and related or neighboring rights to this workby associating CC0 with it.