Generated by SassMeister.com.

SassMeister-input.scss

// ----
// Sass (v3.4.9)
// Compass (v1.0.1)
// ----

// set pixel reference base
$pixelBase: 16 !default;

// strip the unit of measure and return it
@function parseInt($n) {
    @return $n / 1;
}

// convert to rem
@function rem-ize($value, $base-value: $pixelBase)  {
    $value: parseInt($value) / parseInt($base-value) * 1rem;
    @if ($value == 0rem) { $value: 0; } // turn 0rem into 0
    @return $value;
}

// output values in pixels or in rems
@function unit-calc($values, $base-value: $pixelBase) {
    $list: ();
    // if '$ie-lt9' is set to true, convert unit to pixel
    @if ($ie-lt9) {
        @each $i in $values {
            $val: parseInt($i);
            // if value equals '0' or is not a number, just echo the value (handy for 'auto')
            @if ($val == 0 or type-of($val) != "number") {
                $list: append($list, $val);
            // gimme those pixels!
            } @else {
                $list: append($list, $val + px);
            }
        }
    // if '$ie-lt9' is set to false, convert unit to rem
    } @else {
        $max: length($values);
        @if $max == 1 {
    	      @return rem-ize(nth($values, 1), $base-value);
        }
        @for $i from 1 through $max {
            $val: parseInt($i);
            $list: append($list, rem-ize(nth($values, $val), $base-value));
        }
    }
    @return $list;
}

$ie-lt9: true;

.test {
  margin: unit-calc(4 4 8 0);
}

SassMeister-output.css

.test {
  margin: 4px 4px 8px 0;
}