046 capture existing struct

// Test: Capture from existing value — BLOCK FORM.
//
// `~capture { entity }` — a block holding a single bare expression — binds to
// an existing value instead of building a new struct cell. (Open call,
// flagged 2026-06-11: this replaces the old `~capture(entity)` parens form so
// capture has exactly ONE argument shape: the source block.)
// `captured { field: expr }` updates just that field, preserves others.

~import std/io
~import std/control

const std = @import("std");

const Entity = struct {
    id: u32,
    health: i32,
    pos_x: i32,
};

~event print-health { value: i32 }

~proc print-health|zig {
    std.debug.print("{d}\n", .{value});
}

const entity = Entity{
    .id = 42,
    .health = 100,
    .pos_x = 10,
};

~capture { entity }
! as acc |> for(&[_]i32{10, 20, 30})
    ! each damage |> captured { health: acc.health - damage }
| captured final |> print-health(value: final.health)