<===> input.scss
$quoted_list: "foo", "bar", "baz";
$unquoted_list: foo, bar, baz;

foo {
  foo: #{foo, bar, baz};
  foo: #{"foo", "bar", "baz"};
  foo: #{$quoted_list};
  foo: #{$unquoted_list};
}

<===> output.css
foo {
  foo: foo, bar, baz;
  foo: foo, bar, baz;
  foo: foo, bar, baz;
  foo: foo, bar, baz;
}