Local grid support for Susy

_grid.scss

@import "susy";

$grid-info-stack: ();

@function _stack_push($list, $item) {
  @return join($item, $list);
}

@function _stack_top($list) {
  @return nth($list, 1);
}

@function _stack_pop($list) {
  @if length($list) <= 1  { @return (); }
  $new-list: ();
  @for $i from 2 through length($list) {
    $new-list: join($new-list, nth($list, $i))
  }
  @return $new-list;
}

@function local-grid($t:12, $w:4em, $g:1em, $sg:false) {
  @if not $sg {
    $sg: $g;
  }
  $grid-info-stack: _stack_push($grid-info-stack, $side-gutter-width);
  $grid-info-stack: _stack_push($grid-info-stack, $gutter-width);
  $grid-info-stack: _stack_push($grid-info-stack, $col-width);
  $grid-info-stack: _stack_push($grid-info-stack, $total-cols);
  $total-cols: $t;
  $col-width: $w;
  $gutter-width: $g;
  $side-gutter-width: $sg;
  @return 0;
}

@function local-grid-pop() {
  $total-cols: _stack_top($grid-info-stack);
  $grid-info-stack: _stack_pop($grid-info-stack);
  $col-width: _stack_top($grid-info-stack);
  $grid-info-stack: _stack_pop($grid-info-stack);
  $gutter-width: _stack_top($grid-info-stack);
  $grid-info-stack: _stack_pop($grid-info-stack);
  $side-gutter-width: _stack_top($grid-info-stack);
  $grid-info-stack: _stack_pop($grid-info-stack);
  @return 0;
}

@mixin local-grid($t:12, $w:4em, $g:1em, $sg:false) {
  $ignore: local-grid($t, $w, $g, $sg);
}

@mixin local-grid-pop {
  $ignore: local-grid-pop();
}

#testinggrid {
  @include local-grid(6);
  .a { width: columns-width(); }
  @include local-grid(20);
  .b { width: columns-width(); }
  @include local-grid-pop;
  .c { width: columns-width(); }
  @include local-grid-pop;
  .d { width: columns-width(); }
}