.calc(@property, @calculation) {
    @{property}: -webkit-calc(~'@{calculation}');
    @{property}:    -moz-calc(~'@{calculation}');
    @{property}:         calc(~'@{calculation}');
}

.calc(@property, @calculation, @fallback) {
    @{property}: @fallback;
    .calc(@property, @calculation);
}