Generated by SassMeister.com.

SassMeister-input.scss

// ----
// Sass (v3.3.0.rc.5)
// Compass (v1.0.0.alpha.18)
// ----

@import "compass";

@mixin z-index($map){
 @each $element, $value in $map {
    #{$element} {
      z-index: $value;
    } 
  }
}

@include z-index((".below": -1, ".middle": 0, ".above": 1));

SassMeister-output.css

.below {
  z-index: -1;
}

.middle {
  z-index: 0;
}

.above {
  z-index: 1;
}