<===> input.scss
$count: 0;

@function counter() {
  $count: $count + 1 !global;
  @return $count;
}

$map: (
  counter(): 'bar',
  counter(): 'foo',
);

.foo {
  content: inspect($map);
}
<===> output.css
.foo {
  content: (1: "bar", 2: "foo");
}