About less loop, throw error

Question

.loop (@start, @end, @step, @className,@propertyName) when (@start < @end) {
  .@{className}-@{start} {
    @{propertyName}: @start * 1px;
  }
  .loop (@start + @step, @end, @step, @className, @propertyName);
}


.loop(12,48,2,fs,font-size);

I want loop css common class,but throw Error,I don't where the error is on. for example:

.fs-12{
font-size:12px;
}

.fs-13{
font-size:13px;
}

.mt-13{
margin-top:13px;
}

Answer 1

.loop (@start, @end, @step, @className,@propertyName) when (@start < @end) {
  .@{className}-@{start} {
    @{propertyName}: (@start * 1px);
  }
  .loop ((@start + @step), @end, @step, @className, @propertyName);
}



 .loop(12,48,2, fs, font-size);