Dynamic letter-spacing with LESS based on font-size

.letter-spacing (@letter-spacing) when (@font-size >= 36px) {
    letter-spacing: -2px;
}

.letter-spacing (@letter-spacing) when (@font-size < 36px) {
    letter-spacing: 0px;
}

.font-size (@font-size: @baseFontSize) {
    @pxFontValue: (@font-size / @baseFontSize);
    @pxLineHeightValue: (@font-size / @baseFontSize) * 1.5;
    font-size: @font-size * 1px;
    line-height: @font-size * 1.5 * 1px;
    font-size: ~"@{pxFontValue}rem";
    line-height: ~"@{pxLineHeightValue}rem";
    .letter-spacing(@font-size);
}