Simple Grid System in SCSS with Mixins

/**
 * Simple 960 Grid System
 *
 * Adjust grid_width (max width), grid_col (total columns), and 
 * grid_gut (gutter) to perfection.
 *
 * @note:   Consider base-8 widths for optimal image rendering; 
 *          or golden ratios; or Villard Diagrams for perspective grids.
 *
 * @see:    http://smashingmagazine.com/2010/02/09/applying-mathematics-to-web-design/, 
 *          http://thegridsystem.org/tags/golden-ratio/,
 *          http://danielecapo.com/wp/2009/05/04/villard-diagram/,
 *          http://code.google.com/p/the-golden-grid/
 *
 * @usage:  div.grid-12>div.row>(div.columns-6+div.columns+6), etc.
 */
 
/* Core Settings */
 
$grid_width : 960px;
$grid_col   : 12;
$grid_gut   : 20px;
body { min-width: $grid_width; }
 
/* Grid Container */
 
.grid-#{$grid_col} { 
 
  margin-left: auto; 
  margin-right: auto; 
  width: $grid_width;
 
  /* Grid System Classes */
 
  @for $i from 1 through $grid_col {
    .columns-#{$i} { display: inline; float: left; margin-left: $grid_gut / 2; margin-right: $grid_gut / 2; }
    .push-#{$i}, .pull-#{$i} { position: relative; }
    .columns-#{$i} { width: ( ($grid_width / $grid_col - $grid_gut) * $i ) + (($i - 1) * $grid_gut); }
    .prefix-#{$i} { padding-left: $grid_width / $grid_col * $i; }
    .suffix-#{$i} { padding-right: $grid_width / $grid_col * $i; }
    .push-#{$i} { left: $grid_width / $grid_col * $i; }
    .pull-#{$i} { right: $grid_width / $grid_col * $i; }
  }
 
  .row {
    zoom: 1;
    &:before, &:after {
      content: "";
      display: table;
    }
    &:after {
      clear: both;
    }
  }
 
  /* Grid Resets */
 
  .alpha { margin-left: 0; } // no left margin
  .omega { margin-right: 0; } // no right margin
 
  /* Grid System Mixins */
 
  @mixin row() {
    @extend .row;
  }
 
  @mixin columns($col: 1) {
    @extend .columns-#{$col};
  }
 
  @mixin push($col: 1) {
    @extend .push-#{$col};
  }
 
  @mixin pull($col: 1) {
    @extend .pull-#{$col};
  }
 
  @mixin prefix($col: 1) {
    @extend .prefix-#{$col};
  }
 
  @mixin suffix($col: 1) {
    @extend .suffix-#{$grid_col};
  }
 
  @mixin alpha() {
    @extend .alpha;
  }
 
  @mixin omega() {
    @extend .omega;
  }
 
}// Grid Container