system/host/fidl/examples/test.fidl2

library test;

struct Point {
    int32 x;
    int32 y;
};

enum Direction : uint32 {
    Up = 0;
    Down = 1;
    Left = 2;
    Right = 3;
};

struct ArraysOfPoints {
    array<Point>:4 p;
    ArraysOfPoints? more_points;
};

union Points {
    Point one_point;
    ArraysOfPoints many_points;
};

const uint32 NumberOfDirections = 4;

interface Drawing {
    1: Draw(Point p, Direction d);
    2: DrawLots(Points ps);
    3: -> DrawSucceeded(uint32 draws);
};