ColumnsMixin.scss

@mixin columns ($span: $cols of $cont-cols after $shift clearing $clear, $display: block ) {
  $cols: nth($span, 1);
  $cont-cols: nth($span, 3); 
  $shift: nth($span, 5);
  $clear: nth($span, 7);

  @include span-columns( $cols of $cont-cols, $display );
  @include shift($shift);
  @if $clear != 0 {
    margin-right: ($clear * flex-gutter()) + flex-grid($clear);
  }
}

UsageExample.scss

// This will make the div 6 columns wide, with 3 columns of padding on either side.
foo {
  @include columns ( 6 of 12 after 3 clearing 3);
}