Generated by SassMeister.com.

SassMeister-input.scss

// ----
// Sass (v3.3.4)
// Compass (v1.0.0.alpha.18)
// Bourbon (v)
// ----

@import "bourbon/bourbon";

.block {
  width: calc(50% - #{em(200)});
}

@mixin calc($attr, $value, $base: 100%, $operator: '-', $tb-property: null) {
  @if $tb-property == 0 {
    #{$attr}: 20px calc(#{$base} #{$operator} #{$value});
  } @else if $tb-property != 0 {
    #{$attr}: calc(#{$base} #{$operator} #{$value});
  }
}

.block {
  @include calc(width, em(50), '50%', '+', $tb-property: 0);
}

.brick {
  @include calc(margin, em(10), $operator: '*')
}

@mixin van {
  color: black;
  windows: tinted;
  lincense: Washington;
  &.seats {
    seats: 10;
    color: black;
    @content;
    
  }
}

.my-van {
  @include van;
}

.your-van {
  @include van {
    heated: yes;
    fabric: cloth;
    electric: no;
  }
  
}

SassMeister-output.css

.block {
  width: calc(50% - 12.5em);
}

.block {
  width: 20px calc(50% + 3.125em);
}

.brick {
  margin: calc(100% * 0.625em);
}

.my-van {
  color: black;
  windows: tinted;
  lincense: Washington;
}
.my-van.seats {
  seats: 10;
  color: black;
}

.your-van {
  color: black;
  windows: tinted;
  lincense: Washington;
}
.your-van.seats {
  seats: 10;
  color: black;
  heated: yes;
  fabric: cloth;
  electric: no;
}