004 dynamic shape

// TEST: kernel.pairwise basic iteration
//
// k comes from the continuation binding | kernel k |>
// k.X refers to kernel_k[i]
// k.other.X refers to kernel_k[j]

~import "$std/kernel"

// This needs to be module scoped
~std.kernel:shape(Body) {
    id: u32,
    x: f64,
    y: f64,
    mass: f64,
}

// Pairwise: each body accumulates mass from its "other" pair
// Pairs: (0,1), (0,2), (1,2)
// Body 0: 1 + 2 + 3 = 6
// Body 1: 2 + 3 = 5
// Body 2: 3 (unchanged)
~std.kernel:initialize(Body) {
    { id: 1, x: 0.0, y: 0.0, mass: 1.0 },
    { id: 2, x: 1.0, y: 0.0, mass: 2.0 },
    { id: 3, x: 2.0, y: 0.0, mass: 3.0 },
} | kernel k |> std.kernel:pairwise { k.mass += k.other.mass }
    | kernel s |> std.io:print.blk {
        mass[0]={{s[0].mass}} mass[1]={{s[1].mass}} mass[2]={{s[2].mass}}
    }