IMO, the biggest problem is the extra indirection, not the raw lines of code. As for names, the problem is that he is forced to make a new callback whenever he

IMO, the biggest problem is the extra indirection, not the raw lines of code. As for names, the problem is that he is forced to make a new callback whenever he does an IO operation and then needs to make up a name for it on the spot. Ideally you should never be forced to split code into functions unless you actually want to do so and when you can choose where to create functions its much easier to create good abstractions and good names.