A nonempty, immutable sequence of values. A sequence of values may be formed using braces:

value worlds = { "hello", "world" };
value cubes = { for (n in 0..100) n**3 };

The union type Empty|Sequence<Element>, abbreviated Element[], represents a possibly-empty sequence. The if (nonempty ...) construct may be used to obtain an instance of Sequence from a possibly-empty sequence:

Integer[] nums = ... ;
if (nonmpty nums) {
    Integer first = nums.first;
    Integer max = max(nums);
    Sequence<Integer> squares = nums.collect((Integer i) i**2));
    Sequence<Integer> sorted = nums.sort(byIncreasing((Integer i) i));
}

Operations like first, max(), collect(), and sort(), which polymorphically produce a nonempty or non-null output when given a nonempty input are called emptiness-preserving.