You cannot define a nested function within an "if" or "while" or "switch" or "try/catch" or any other control structure.
Note, by the way, that if your function definition did succeed there, then you would not have invoked the function. And if you did invoke the function, then you would have ended up calling sort() many times. You should not be using sort() at all.
At the time that you are combining two sub-arrays after having sorted the two sub-arrays, then you know that each half has been sorted. That makes it less expensive to do the merge, using techniques such as insertion sort.
