1<===> input.scss
2@function test($pos) {
3  @return test-#{$pos};
4}
5
6.foo {
7  content: test(str-slice('scale-0', 7));   // Nope
8  content: test-#{str-slice('scale-0', 7)}; // Yep
9}
10<===> output.css
11.foo {
12  content: test-0;
13  content: test-0;
14}
15