Chris Smith
Computability is just a distraction here. The problem isn't whether "getAnIntFromUser" is computable... it is whether it's a function at all! Even uncomputable functions are first and foremost functions, and not being computable is just a property that they have. Clearly this is not a function at all. It doesn't even have the general form of a function: it has no input, so clearly it can't map each input value to a specific output value. Now, since it's not a function, it makes little sense to even try to talk about whether it is computable or not (unless you first define a notion of computability for something other than functions).
Of course getAnIntFromUser is not a function. It is an instruction to computer. Think of IO as a form of writing instructions to some worker (essentially, the kernel, which in its turn uses processor's io ports). You are asking this “worker” to change some global state. Thus, your function “f” is a function indeed, which generates a list of instructions to kernel, according to given number.