Generated by SassMeister.com.

SassMeister-input.scss

// ----
// Sass (v3.4.4)
// Compass (v1.0.1)
// ----

//From:http://codepen.io/qiu8310/pen/EGyei
// 在 list 中第 index 个字符串后加上 value 字符串
// list: (a b c d)   index: 3,  value: _hack  =>  (a b c_hack d)
@function list-nth-append($list, $index, $value) {

  $result: ();
  $index: if($index < 0, length($list) + $index + 1, $index);

  @for $i from 1 through length($list) {
    @if $i == $index {
      $result: append($result, nth($list, $i) + $value);
    }

    @else {
      $result: append($result, nth($list, $i));
    }
  }

  @return $result;
}


@mixin on-parent-status($status) {
  $new-selectors: ();
  $selectors: &;
  $status: unquote($status); // 去掉可能存在的 引号(" or ')

  @if $selectors {
    // @debug length($selectors);  // $selectors 是一个 逗号 分开的数组
    @each $selector in $selectors {
      $len: length($selector);  // $selector 是一个 空格 分开的数组
      @if $len < 2 {
        @error "`parent-status` current selector `#{$selector}` no parent selector";
      }

      $selector: list-nth-append($selector, -2, $status);

      $new-selectors: append($new-selectors, $selector, comma);
    }

    @at-root #{$new-selectors} {
      @content;
    }

  } @else {
    @error "`parent-status` Should not at root!";
  }

}


body {
  width: 600px;
  margin: 0 auto;
}



.tab {
  a {
    display: inline-block;
    padding: 10px 60px;
    cursor: pointer;    
    
    &:hover {
      background: #AAA;
    }
    
    i {
      margin-left: 10px;
      
      @include on-parent-status(':hover') {
        color: red;
      }
    }
  }
  
  .home_link, .about_link {
    i {
      @include on-parent-status(':hover') {
        background: green;
      }
    }
  }
  
}

SassMeister-output.css

body {
  width: 600px;
  margin: 0 auto;
}

.tab a {
  display: inline-block;
  padding: 10px 60px;
  cursor: pointer;
}
.tab a:hover {
  background: #AAA;
}
.tab a i {
  margin-left: 10px;
}
.tab a:hover i {
  color: red;
}
.tab .home_link:hover i, .tab .about_link:hover i {
  background: green;
}