Traversing the sweeps of a family of waveforms to calculate the max turn-on time

Hello:

I am trying to make a turn-on time measurement on a transient voltage.  This measures how long it takes for a certain voltage to reach a certain Y-value threshold, Yth.  However I would like to create a function that can take a family of waveforms (set of corners) and give me the maximum of the turn-on times over the family of waveforms.  Here is what I have so far with comments explaining how I would like the function to work:

;apGetMaxTurnOn(famIn tmin tmax Yth)
; INPUTS
; famIn - wave or family of waves to measure the turn-on time.
; tmin - minimum time
; tmax - maximim time
; Yth - Y value threshold to get the period.
; Returns a list with the following elements
; '(maxWaveform maxT cornerInfo)
; maxWaveform: Waveform object with the max turn-on period
; maxT - Max turn-on period
; cornerInfo - A list with the corner information. One entry for each sweep name in the family of curves.
; EXAMPLE
; ; Calculate the max turn-on time to 1.5v for famIn which is between 0us and 20us
; turnOnList = apGetMaxTurnOn(nthelem(6 out) 0 20u -2.5)
procedure(apGetMaxTurnOn(famIn tmin tmax Yth)
let(()
xVal=cross(clip(famIn tmin tmax) Yth 1 "either" nil nil nil )
;xVal=cross(nthelem(6 out) -2.5 1 "either" nil nil nil )
when(drIsWaveform(xVal)
1 ; TO DO: Return the turn-on list for the turn-on time of the single waveform
)
when(famIsFamily(xVal)
1 ; TO DO: Return the turn-on list list as described above for the trace with the max turn-on time
))
)

I have figured out how to get to the data by  repeatedly using drGetWaveformYVec and drGetElem:

Note: xVal is a family of waveforms with the lowest waveform in the sweep hierarchy having the turn-on period for one of the traces.

drGetElem(drGetWaveformYVec(drGetElem(drGetWaveformYVec(drGetElem(drGetWaveformYVec(xVall) 0)) 0)) 0)

However I would like the function to work with any number of sweep parameters but I'm not sure how to traverse an unknown number of sweep parameters.  If I knew the number of sweep parameters I could use a nested loop, however the family of waveforms that is input to the function could have an arbitrary number of sweeps. 

What's the best way to traverse a family of waveforms to calculate the max turn-on period?  Could you please provide some example code?

I am using IC6.1.7.

-Curtis