看编译结果：http://SassMeister.com/gist/cc9c6604b95b767fecb3

link-status.scss

@import 'base.sass/+';

$link-status: (
  link: (
    color: #428bca,
    line: none
  ),
  hover: (
    // color: defaults to darken(link.color, 15%),
    line: underline
  )
);

a {
  color: map-get($link-status, link, color);
  text-decoration: map-get($link-status, link, line);

  &:hover {
    color: map-get($link-status, hover, color)
           or
           darken(map-get($link-status, link, color), 15%);
    text-decoration: map-get($link-status, hover, line);
  }
}