$gutter-width: 10px
$column-width: 40px

=column-base
  float: left
  margin:
    left: $gutter-width
    right: $gutter-width

=last-column
  margin-right: 0

=first-column
  margin-right: 0

=column($columns, $first: false, $last: false)
  @extend column-base
  @if $first
    @extend first-column
  @if $last
    @extend last-column
  width: $column-width * $columns - $gutter-width

=three-column-layout($left-cols, $middle-cols, $right-cols)
  =full-width
    +column($left-cols + $middle-cols + $right-cols, $first: true, $last: true)
  =header
    @extend full-width
  =footer
    @extend full-width
  =left-column
    +column($left-cols, $first: true)
  =middle-column
    +column($middle-cols)
  =right-column
    +column($right-cols, $last: true)
  @yield

body.standard
  +three-column-layout(5,12,7)
    #footer
      +footer
    #header
      +header
    #sidebar
      +left-column
    #content
      +middle-column
    #ads
      +right-column