oceanEval statement in monte carlo simulation in spectre

Hello all,

I am trying to finish my course project by spectre. I am trying to run
Monte Carlo simulation through my netlist, and measure the propagation
delay across a gate.  I search through all the accessible spectre
do***ents about Monte Carlo simulation,  they all do measurement
through oceanEval statement.

ex****t somesignal=oceanEval("some expression")

I couldn't find any do***entation on how oceanEval was supposed to be
used, and the some expression in the brackets looked like it was from
spectreMDL, so my code ended up looking like:

m1 montecarlo saveprocessparams=yes processscalarfile="../process.dat"

+        numruns=30 variations=process seed=10{
         dcop1 dc
         tran1 tran start=0 stop=0.2ns step=0.01ns
         ex****t nor1in1=oceanEval("deltax(sig1=nor1in1, sig2=nor1out,
dir1='rise, n1=1, start1=0, thresh1=0.75, dir2='fall, n2=1, start2=0,
thresh2=0.75)")

}

However, when I type "spectre myinputfile" in the terminal, some
errors display in the terminal like:

Error found by spectre during circuit read-in.
    "gatesizing.spi" 105: Function `oceaneval' is undefined or is used
        recursively.
"gatesizing.spi" 105: VCVS (ex****t) needs 4 nodes (0 given).

How can I measure the propagation delay in a Monte Carlo simulation
without going through the gui? All I need are the values; I'll run
the rest through Matlab.

Thanks!
Jerry