space-generator

@iterations: 15;
@step: 5;

.mixin-loop(@i) when (@i > 0) {

  @space-val:  @i * @step;

  .space-@{space-val} {
    height: @space-val * 1px;
  }

  .mixin-loop(@i - 1);
}

.mixin-loop(@iterations);