$values: ();

foo {
    $duplicates: 0;
    $num: random();
    $is-number: type-of($num) == number;
    $is-within-range: $num >= 0 and $num < 1;
    $values: append($values, $num);

    @for $i from 1 through 1000 {
      $num: random();
      $is-number: $is-number and type-of($num) == number;
      $is-within-range: $is-within-range and $num >= 0 and $num < 1;
      @if (index($values, $num) != null) { $duplicates: $duplicates + 1; }
      $values: append($values, $num);
    }

    is-defined: $num != "random()";
    is-number: $is-number;
    is-within-range: $is-within-range;
    is-random: $duplicates < 25;
}