// The idea is to postprocess to match out
// e.g. out="a, b, c"
// and f=FJoin(", ")

static class LPost extends LearnerImpl {
  ReversibleFunction f;
  Learner base;
  
  *(ReversibleFunction *f, Learner *base) {}
  
  public void processInOut(Object in, Object out) {
    out = f.unprocess(out);
    base.processInOut(in, out);
  }
  
  public Object processIn(Object in) {
    in = base.processIn(in);
    in = f.process(in);
    return in;
  }
  
  public void toJava(Code code) {
    base.toJava(code);
    f.toJava_process(code);
  }
}

Began life as a copy of #1000511