superbem.scss

@mixin block($name) {
    .#{$name} {
        $block:    $name !global;
        $this:     $name !global;

        @content;

        $block:    null !global;
        $this:     null !global;
    }
}

@mixin b($name) {
    @include block($name);
}

@mixin element($name) {
    $this: #{$block}__#{$name} !global;

    @if (global-variable-exists(element) and $element) or (global-variable-exists(modifier) and $modifier) {
        $element: #{$block}__#{$name} !global;

        .#{$element} {
            @content;
        }
    } @else {
        $element: #{$block}__#{$name} !global;

        @at-root .#{$element} {
            @content;
        }
    }

    $this:    $block !global;
    $element: null !global;
}

@mixin e($name) {
    @include element($name);
}

@mixin modifier($name) {
    @at-root .#{$this}--#{$name} {
        $modifier: #{$this}__#{$name} !global;

        @extend .#{$this} !optional;
        @content;

        $modifier: null !global;
    }
}

@mixin m($name) {
    @include modifier($name);
}

@mixin is-after($scope) {
    $expression: null;

    @if str-index(#{$scope}, '.') {
        $expression: '#{$scope} + .#{$this}';
    } @else if str-index($scope, '__') {
        $expression: '.#{$scope} + .#{$this}';
    } @else {
        $expression: '.#{$block}__#{$scope} + .#{$this}';
    }

    @at-root #{$expression} {
        @content;
    }
}

@mixin is-preceded-by($scope) {
    @if str-index(#{$scope}, '.') {
        $expression: '#{$scope} ~ .#{$this}';
    } @else if str-index($scope, '__') {
        $expression: '.#{$scope} ~ .#{$this}';
    } @else {
        $expression: '.#{$block}__#{$scope} ~ .#{$this}';
    }

    @at-root #{$expression} {
        @content;
    }
}

@mixin is-inside($scope) {
    @if str-index(#{$scope}, '.') {
        $expression: '#{$scope} > .#{$this}';
    } @else if str-index($scope, '__') {
        $expression: '.#{$scope} > .#{$this}';
    } @else {
        $expression: '.#{$block}__#{$scope} > .#{$this}';
    }

    @at-root #{$expression} {
        @content;
    }
}