<===> input.scss
$map: (foo: 'b', bar: c);
$list: ('d', e);

a {
  #{map-get($map, foo)} & {
      foo: bar;
  }
  #{map-get($map, bar)} & {
      foo: bar;
  }

  #{nth($list, 1)} & {
      foo: bar;
  }

  #{nth($list, 2)} & {
      foo: bar;
  }
}

<===> output.css
b a {
  foo: bar;
}
c a {
  foo: bar;
}
d a {
  foo: bar;
}
e a {
  foo: bar;
}