# False and nil are false.
unless (false) {
    print("false"); # expect: false
}
unless (nil) {
    print("nil"); # expect: nil
}
# Everything else is true.
unless (true) {
    print("bad");
} else {
    print(true); # expect: true
}
unless (0) {
    print("bad");
} else {
    print(0); # expect: 0
}
unless ("") {
    print("bad");
} else {
    print("empty"); # expect: empty
}