// to next.
JVar currentIndex = eval.decl(generator.getModel().INT, "currentIndex" + listNum, JExpr.lit(-1));
eval._while( //
currentIndex.lt(desiredIndex) //
.cand(list.invoke("next"))).body().assign(currentIndex, currentIndex.plus(JExpr.lit(1)));
JBlock ifNoVal = eval._if(desiredIndex.ne(currentIndex))._then().block();
if (out.isOptional()) {
ifNoVal.assign(out.getIsSet(), JExpr.lit(0));