Generated by SassMeister.com.

SassMeister-input.scss

// ----
// Sass (v3.4.12)
// Compass (v1.0.3)
// ----

@function foo($keyword) {
  @if $keyword == extra {
    @return "true";
  } @elseif $keyword == extra thin {
    @return "true2";
  } @else {
    @return "false";
  }
}

.foo {
  font-family: foo(extra thin);
}

SassMeister-output.css

.foo {
  font-family: "true2";
}