Maybe the missing link there for you is : which is "else".I enjoyed a lot the Formula Parser section It is easy to understand as well, except one thing I couldn't understand well. The 'if' or '?' function. I know them by themselves and I know how to use them, but how to compute the result?!
Take the example formula preset "squarify" which removes even harmonics from the wavetable via FFT:
((q%2)==1)?in:0
This is saying, if the FFT harmonic (q) is odd (%2==1, e.g. bin 1,3,5) then allow it to remain (in) or else become silent (0).