009 mixed literal comprehension rows

// RED PIN (type-system design walk, 2026-07-06/07). The "reads
// naturally" guarantee: a struct block is a list of FIELD PRODUCERS —
// a literal field row is the trivial producer, a comprehension clause
// is the generative one, MIXED FREELY in one block. A row is a
// comprehension clause iff it opens with `<binder> over`; otherwise it
// is a literal field. The common case stays byte-for-byte what any
// systems programmer expects; the power is an optional row form, not a
// different construct. Spellings PROVISIONAL.

~import std/types
~import std/io

const std = @import("std");

~std/types:struct(Particle) {
    id: i64,
    i over 0..2 -> pos{i}: f64
    i over 0..2 -> vel{i}: f64
    alive: bool,
}

~event main {}

~proc main|zig {
    const p = Particle{
        .id = 1,
        .pos0 = 0.5, .pos1 = 1.5,
        .vel0 = 0.0, .vel1 = -9.8,
        .alive = true,
    };
    std.debug.print("p{d} at ({d:.1}, {d:.1})\n", .{ p.id, p.pos0, p.pos1 });
}

~main()