.demo (light, @color) {
  color: lighten(@color, 10%);
}
.demo (@_, @color) {
  display: block;
}

@switch: light;

.class {
  .demo(@switch, #888);
}

// by arity

.mixin () {
    zero: 0;
}
.mixin (@a: 1px) {
    one: 1;
}
.mixin (@a) {
    one-req: 1;
}
.mixin (@a: 1px, @b: 2px) {
    two: 2;
}

.mixin (@a, @b, @c) {
    three-req: 3;
}

.mixin (@a: 1px, @b: 2px, @c: 3px) {
    three: 3;
}

.zero {
    .mixin();
}

.one {
    .mixin(1);
}

.two {
    .mixin(1, 2);
}

.three {
    .mixin(1, 2, 3);
}

//

.mixout ('left') {
    left: 1;
}

.mixout ('right') {
    right: 1;
}

.left {
    .mixout('left');
}
.right {
    .mixout('right');
}

//

.border (@side, @width) {
    color: black;
    .border-side(@side, @width);
}
.border-side (left, @w) {
    border-left: @w;
}
.border-side (right, @w) {
    border-right: @w;
}

.border-right {
    .border(right, 4px);
}
.border-left {
    .border(left, 4px);
}

//


.border-radius (@r) {
    both: @r * 10;
}
.border-radius (@r, left) {
    left: @r;
}
.border-radius (@r, right) {
    right: @r;
}

.only-right {
    .border-radius(33, right);
}
.only-left {
    .border-radius(33, left);
}
.left-right {
    .border-radius(33);
}

.hola(hello, @hello...) {
	color: blue;
}

#hola {
	.hola(hello, world);
}

.resty(@hello, @world, @the_rest...) {
	padding: @hello @world;
	rest: @the_rest;
}

.defaults(@aa, @bb:e343, @cc: "heah", ...) {
	height: @aa;
}

#defaults_1 {
	.defaults(one);
	.defaults(two, one);
	.defaults(three, two, one);
	.defaults(four, three, two, one);
}


.thing() { color: green; }
.thing(...) { color: blue; }
.thing { color: red; }

#aa {
	.thing();
}

#bb {
	.thing;
}


#cc {
	.thing(1);
}