The Filter Parser
  
The filter expression parser knows how to take an expression of the form 'PID != ~777 && PARAMS[1] + 3 > ("foo" in ("boo", "bee", "bah"))' and build a filter tree suitable for passing to the kernel, while maintaining operator precedence. 

The basic algorithm is taken from the dragon book and was extended for our grammar in several sleepless nights. It uses one function for each precedence level, where each function looks like this: