Sean suggested I subscribe here and ask the question rather than using the list [log in to unmask] So, I am trying an experiment where I do not want to evaluate s-expressions as in classic genetic programming, but to evaluate instructions or mnemonics(?) as in FORTH or assembler. I can easily write the FORTH-like evaluator within the objective function of my code. What I need help with is the proper/best way to have something like the IntegerVectorIndividual that has a variable, rather than a fixed, genome size. Mike