.sass syntax grid system from http://viget.com/inspire/building-a-nested-responsive-grid-with-sass-compass

gistfile1.sass

$cols: 12
$gutter: 2%
 
$one_col: (100% - ($gutter * ($cols - 1))) / $cols
 
@mixin cols($num)
    width: ($one_col * $num) + ($gutter * ($num - 1))

 
@mixin sub_cols($num_child, $num_parent)
    $parent_size: ($one_col * $num_parent) + ($gutter * ($num_parent - 1))
    $child_size: ($one_col * $num_child) + ($gutter * ($num_child - 1))
    margin-left: ($gutter / $parent_size) * 100%
    width: ($child_size / $parent_size) * 100%

.row
    #{enumerate('.span', 1, $cols, '')}
        float: left
        margin-left: $gutter
 
    @for $i from 1 through $cols
        .span#{$i}
            @include cols($i)
 
            @for $j from 1 through ($i - 1)
                .span#{$j}
                    @include sub_cols($j, $i)

    > :first-child, .row > :first-child
        margin-left: 0