(w1#(NN)) (w1#(w1 & "ing")) (eval(w1))
This tiny piece of code shows you how you can turn a NOUN (NN) into a GERUND (VBG).
The first line: (w1#(NN))
w1 is our variable. We assign with the # operator. NN is the function which generates a random noun from the dictionary.
Then we reassign w1 = w1 + "ing" which in SMUP is..
(w1#(w1 & "ing"))