1<===> input.scss
2@function foo($foo) {
3  @return $foo;
4}
5
6@function data($foo) {
7  @return '[data-' + $foo + ']';
8}
9
10#{foo(foo)} {
11  #{data('bar')} {
12    baz: bam;
13  }
14}
15
16<===> output.css
17foo [data-bar] {
18  baz: bam;
19}
20