bem.css.sass

@mixin block($name)
  @at-root .#{$name}
    @content

@mixin element($names...)
  $selector: ()
  @each $name in $names
    $selector: append($selector, unquote('#{&}__#{$name}'), comma)
  @at-root #{$selector}
    @content

@mixin modifier($names...)
  $last-scope: &
  $selector: ()
  @each $name in $names
    $selector: append($selector, unquote('#{&}--#{$name}'), comma)
  @at-root #{$selector}
    @extend #{$last-scope}
    @content