Integer arg1 = trackInteger(expr.getArg(0));
Integer arg2 = trackInteger(expr.getArg(1));
UnaryOperation op;
if (arg1 != null) {
if (arg2 != null) {
op = new Replace1((char) arg1.intValue(), (char) arg2.intValue());
} else {
op = new Replace2((char) arg1.intValue());
}
} else {
if (arg2 != null) {