How to get the current selector in Sass

SassMeister-input.scss

// ----
// Sass (v3.4.14)
// Compass (v1.0.3)
// SassyLists (v2.2.1)
// ----

@import "SassyLists";

@function last-sels() {
    $sel: &; $out: ();
    @each $list in $sel {
      $curr: nth($list, length($list));
      @if not index($out, $curr) {
        $out: append($out, $curr, 'comma');
      }
    }
    @return $out;
}

@function initial-sels() {
    $sel: &; $out: ();
    @each $list in $sel {
      $curr: sl-slice($list, 1,  length($list) - 1);
      @if not index($out, $curr) {
        $out: append($out, $curr, 'comma');
      }
    }
    @return $out;
}

@function sibling-to($siblings, $op: '+'){
  $initials: initial-sels();
  $lasts: last-sels();
  $out: '';
  @for $i from 1 through length($initials) {
    @for $s from 1 through length($siblings) {
      @for $l from 1 through length($lasts) {
        $out: if(($i $s $l) == (1 1 1),
          unquote('#{nth($initials, $i)} #{nth($siblings, $s)} #{$op} #{nth($lasts, $l)}'),
          $out + unquote(', #{nth($initials, $i)} #{nth($siblings, $s)} #{$op} #{nth($lasts, $l)}')
        );   
      }
    }
  }
  @return $out;
}

@mixin sibling-to($args...) {
  @at-root #{sibling-to($args...)} {
    @content;
  }
}

.nested .really p {
  initial: inspect(initial-sels());
  last: inspect(last-sels());
  margin-top: 1rem;
  @at-root #{sibling-to(h1 h2 h3 h4 h5 h6, '~')} {
    margin-top: 0;
  }
}
p + p {
  margin-top: 0;
}

.typo h1, body {
  p {
    margin-top: 1rem;
    @include sibling-to(p) {
      margin-top: 0;
    }
  }
}

SassMeister-output.css

.nested .really p {
  initial: (.nested .really,);
  last: (p,);
  margin-top: 1rem;
}
.nested .really h1 ~ p, .nested .really h2 ~ p, .nested .really h3 ~ p, .nested .really h4 ~ p, .nested .really h5 ~ p, .nested .really h6 ~ p {
  margin-top: 0;
}

p + p {
  margin-top: 0;
}

.typo h1 p, body p {
  margin-top: 1rem;
}
.typo h1 p + p, body p + p {
  margin-top: 0;
}