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
documents about Monte Carlo simulation, they all do measurement
through oceanEval statement.

export somesignal=oceanEval("some expression")

I couldn't find any documentation 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
export 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 (export) 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