Sass+Compass Multiple 'inline-image' background

gistfile1.scss

@mixin data-background($image...){
  $length:length($image);
  @if ($length > 1) {
    $images:null;
    $sizes:null;
    
    @for $i from 1 through $length {
       $images:append($images, inline-image(nth($image, $i)), "comma");
       $sizes:append($sizes, image-size(nth($image, $i)), "comma");
    }
    background-image:$images;
    @include background-size($sizes);
    
  } @else {
    $image:nth($image, 1);
    background-image:inline-image($image);
    @include background-size(image-size($image));
  }
};

//$s = scale
@function image-size($image, $s:2) {
  $width : image-width($image);
  $height: image-height($image);
  @if $s > 1 {
    $width:$width/$s;
    $height:$height/$s;
  }
  @return $width $height;
}

//use
//@include data-background('foo.png', 'bar.png');
//@include data-background('hoge.png');