That's because you're not considering the fact that the complexity of handling movement in each direction will increase -dramatically- as she continues to write

That's because you're not considering the fact that the complexity of handling movement in each direction will increase -dramatically- as she continues to write out the game. If the logic would forever stay a one liner, "increment the y coord!" when the up arrow key is pressed, I would agree with you - keep the case statement and go on your merry way. But that isn't the case, and my wife anticipated that being the case, hence the motivation for her question. Spreading out complex logic into separate functions is usually considered good form. Like every design decision, you have to be wary not to overdo it - but I think my wife was spot on in identifying the need to do so in this case. Putting the case statement aside for a second - you're also overlooking the fact that by using functions in this way the implementation becomes pure. The functions do not mutate anything and are completely oblivious to the fact that they are being used to swap! out the current position of the player for another. Some benefits to writing pure functions include easier testing (you don't have to supply an atom to know if your function works, just call the function) and REPL use is vastly simplified. Additionally, I don't even need a browser or a keyboard handler to see if my movement functions work.