A simple less loop with comments and simple from, to syntax.

gistfile1.css

/* Define two variables as the loop limits */
@from : 0;
@to : 10;

/* Create a Parametric mixin and add a guard operation */
.loop(@index) when(@index =< @to) {

  /* As the mixin is called CSS is outputted */
  div:nth-child(@{index}) {
    top: unit(@index * 100, px);
  }

  /* Interation call and operation */
  .loop(@index + 1);
}

/* the mixin is called, css outputted and iterations called */
.loop(@from);

/*

## Output

div:nth-child(0) {
  top: 0px;
}
div:nth-child(1) {
  top: 100px;
}
div:nth-child(2) {
  top: 200px;
}
div:nth-child(3) {
  top: 300px;
}
div:nth-child(4) {
  top: 400px;
}
div:nth-child(5) {
  top: 500px;
}
div:nth-child(6) {
  top: 600px;
}
div:nth-child(7) {
  top: 700px;
}
div:nth-child(8) {
  top: 800px;
}
div:nth-child(9) {
  top: 900px;
}
div:nth-child(10) {
  top: 1000px;
}


*/