Generated by SassMeister.com.

SassMeister-input.scss

// ----
// libsass (v3.3.2)
// ----

@mixin link($initial-state, $hover: $initial-state, $active: $initial-state, $focus: $initial-state, $visited: $initial-state) {
  $states: (
    'hover': $hover,
    'active': $active,
    'focus': $focus,
    'visited': $visited
  );
  $same-states: ();
  
  @each $state, $color in $states {
    @if ($initial-state != $color) {
      &:#{$state} {
        color: $color;
      }
    } @else {
      $same-states: append($same-states, '&:#{$state}', 'comma');
    }
  }
    
  &, #{$same-states} {
    color: $initial-state;
  }
}

a {
  @include link(red, green, blue)
}

SassMeister-output.css

a:hover {
  color: green;
}

a:active {
  color: blue;
}

a, a:focus, a:visited {
  color: red;
}