pattern matching specialization

concept.sass

@mixin some_sprite($state) {
  background-image: url(...);
  /* etc... */
}
@mixin some_sprite(default) {
  background-position: 0px 18px;
}
@mixin some_sprite(hover) {
  background-position: 18px 18px;
}

// somewhere down the line ..........

.thingy {
  @include some_sprite(default);
}
.thingy:hover {
  @include some_sprite(hover);
}