Top item is popped from the stack and Compared to 0. 0 or 1 is pushed back to the stack where 0 indicates false and 1 indicates true.

See programming note for comparing unlike types.

#prints out 0 (False) to the tracelog
1 eq0 Trace

#prints out 1 (True) to the tracelog
7 8 sub 1 add eq0 Trace