instructions.md

Lilly the Lisp Alien has definitely made a lot of Lasagna with your help. They want to thank you by giving you some leftovers. But first they have some feedback about one of the functions you helped them with.

In this exercise you are going to write some more functions to help Lilly with their Lasagna cooking as well as helping them split the leftovers with you.

You have six tasks, three about improving the existing Lasagna cooking functions and three about splitting the leftovers.

1. Make preparation-time-in-minutes easier to use

Lilly says they found using your preparation-time-in-minutes a little awkward to use since they had to count all the layers before using the functions. Lilly wonders if you could make a version of the function that takes the layers (any number of them) as arguments and then calculate the preparation time based upon how many layers there were? As a reminder, it takes 19 minutes to prepare a single layer.

(preparation-time 'sauce 'cheese 'right-handed-macaroni 'cheese 'sauce
                  'left-handed-macaroni 'sauce 'sauce 'cheese 'cheese)
                  ;; => 190 (because there are 10 layers.)

2. Allow changing the expected oven time

While Lilly's parental-units always cooked their lasagna for 337 minutes, Lilly does admit that other Lisp Aliens like to cook their lasagna for longer or shorter amounts of time.

So it would be good if remaining-minutes-in-oven would not use expected-minutes-in-oven but instead could take an optional parameter to define if the time should be longer, very long, shorter or very short. Longer or shorter means add or subtract 100 from the default time of 337. Very long or very short means add or subtract 200. If no parameter is provided, or the argument is 'normal' then the default value of 337 should be returned.

(remaining-minutes-in-oven)             ;; => 337
(remaining-minutes-in-oven :normal)     ;; => 337
(remaining-minutes-in-oven :shorter)    ;; => 237
(remaining-minutes-in-oven :longer)     ;; => 437
(remaining-minutes-in-oven :very-long)  ;; => 537

3. Lilly remembers another preferred cooking style

Just after you finished that change Lilly remembers that there are some Lisp Aliens that like really short cooking times. Effectively they want it raw. So now the function should return 0 if NIL was the argument as well as the same values as in the previous task.

(remaining-minutes-in-oven)     ;; => 337
(remaining-minutes-in-oven nil) ;; => 0

4. Splitting the leftovers

Now that you've helped improve the lasagna cooking functions there is a lot of lasanga! Lilly wants to repay you for all your help by splitting the leftovers with you. You will need to write a function that takes three parameters: the total amount of leftovers, the number of containers for leftovers Lilly found in their cupboards and the same for you. Because searching for leftover containers may take different amounts of time, and the exact amount of leftovers may be determined while yourself and Lilly are out searching your cupboards you both agree that the function should take the arguments in any order, so as each number is determined you can write it down. When you have all three numbers you can just close the parenthesis on the function call and evaluate it.

The function should return the amount of leftovers which are leftover, that is, the difference between the weight of left-overs and the total number of containers that you and Lilly found.

(split-leftovers :weight 20 :human 10 :alien 5) ;; => 5
(split-leftovers :weight 20 :alien 10 :human 2) ;; => 8
(split-leftovers :alien 12 :weight 20 :human 4) ;; => 4

5. Making assumptions

After a few trips back and forth to your respective cupboards, you both agree that it would be great if the function could just assume that you or Lilly had... say 10 containers if it were not specified.

(split-leftovers :weight 20 :human 5) ;; => 5
(split-leftovers :weight 20 :alien 5) ;; => 5
(split-leftovers :weight 20)          ;; => 0

6. Standard amount of leftovers

Even better the function could assume that there is enough leftovers to fit into the containers. So if the weight is not provided the function should return 'just-split-it. However if the weight is provided and it is nil or 0 then it should return 'looks-like-someone-was-hungry.

(split-left-overs :human 5 :alien 5) ;; => :JUST-SPLIT-IT
(split-left-overs :weight NIL :human 5 :alien 5) ;; => :LOOKS-LIKE-SOMEONE-WAS-HUNGRY