AMCSS selector mixin for SCSS

_am.scss

// ====================================================================
//
// AMCSS SCSS Mixin
// --------------------------------------------------------------------
// Kael Watts-Deuchar @KaelWD
//
// Heavily based on a mixin by @indrekpaas but improved with the
// addition of multiple selectors in one declaration.
//
// Original: https://gist.github.com/indrekpaas/49f466270618d4b8ee7e
// ====================================================================

@mixin am($args...) {
    $prefix : "am-";

    $selectors : ();

    @each $group in $args {

        @if length($group) == 1 {
            $selector : "[#{$prefix}#{$group}]";
            $selectors : append($selectors, $selector, "comma");
        } @else {
            $namespace : nth($group, 1);
            $val : ();
            @for $i from 2 through length($group) {
                $val : append($val, nth($group, $i));
            }
            $selector : "[#{$prefix}#{$namespace}~=\"#{$val}\"]";
            $selectors : append($selectors, $selector, "comma");
        }
    }

    #{$selectors} {
        @content;
    }
}

input.scss

@include am(Block) {
    content : 'Selecting a block';
}

@include am(Block-Child) {
    content : 'Selecting a child element';
}

@include am(Block-Child variant) {
    content : 'Selecting a variant';
}

@include am(First, Second-Child, Third variant, Fourth variant another-variant) {
    content : 'Selecting several blocks and variants at once';
}

output.scss

[am-Block] {
    content: 'Selecting a block';
}

[am-Block-Child] {
    content: 'Selecting a child element';
}

[am-Block-Child~="variant"] {
    content: 'Selecting a variant';
}

[am-First], [am-Second-Child], [am-Third~="variant"], [am-Fourth~="variant another-variant"] {
    content: 'Selecting several blocks and variants at once';
}