SASS : Dynamically Build Ruleset

build-ruleset.scss

@mixin layout($sections, $unit:"%") {
    #content {
        @each $name, $rules in $sections {
            .#{$name} {
                @each $key, $value in $rules {
                    #{$key} : $value
            }
            }
        }
    }
}

$sections: (
  header:  (width: 100%, background: #aaa),
  sidebar: (width: 33%, background: #ccc),
  body:    (width: 67%, background: #ddd),
  footer:  (width: 100%, background: #bbb)
);
@include layout($sections)