Comp 210 Lab 3: Non-empty Lists of Numbers

Solution 1: The base case should describe all lists of length one, the shortest possible non-empty lists:

     ; A non-empty-list-of-numbers is one of
     ;   - (cons f empty)
     ;     where f is a number
     ;   - (cons f r)
     ;     where f is a number, and r is a non-empty-list-of-numbers

In this case, the template looks as follows:

(define (func-for-nelon a-nelon)
   (cond
      [(empty? (rest a-nelon)) ...(first a-nelon)...]
      [else                    ...(first a-nelon)...(func-for-nelon (rest a-nelon))...]))

Solution 2: We could use the definition of (perhaps-empty) list-of-numbers, that we've already seen.
```
     ; A non-empty-list-of-numbers is
     ;   (cons f r)
     ;   where f is a number, and r is a list-of-numbers
```
Here, the template is different, since it must refer to the template for a regular (non-empty) list-of-numbers. In particular, you don't make a recursive call; you think to yourself "Ah, a-nelon contains a (perhaps-empty) list; i'd better call a function for such regular ol' lists":
```
(define (f a-nelon)
   ...(first a-nelon)...(func-for-lon (rest a-nelon))...)
```
To compute the average, what function(s) of general (perhaps-empty) lists do you want to call, as your helper?

usually