pub fn main(world: World) -> Void raises {
    var backing: [4096]u8 = [0; 4096]
    var alloc: FixedBufAlloc = std.mem.fixedBufAlloc(backing)
    let bytes: Maybe<MutSpan<u8>> = std.mem.allocBytes(alloc, 64)
    if bytes.has {
        let buf: MutSpan<u8> = bytes.value
        buf[0] = 7
        if buf[0] == 7 {
            check world.out.write("fixed buf alloc local ok\n")
        }
    }
}