A loop in sass

gistfile1.css

$marginDirections: left, right, bottom, top;
$marginValues: 10, 20, 30, 40, 50, 60;

@for $marginDirection from 1 through length($marginDirections) {
  @for $marginValue from 1 through length($marginValues) {
    .add-#{$marginDirection}-#{$marginValue} {
      margin-#{$marginDirection}: #{$marginValue}px;
    }
  }
}