Recursion: factorial
Recursion: prod
Recursion: product
Recursion: length
Recursion: reverse
Recursion: append (++ operator)
Recursion: insert
Recursion: isort
Recursion: zip
Recursion: drop
Recursion: fibonacci
Recursion: qsort
Recursion: even/odd
Recursion: init
Exercise 06-1: Reimplement ^ for non-negative integers (including 0)
Exercise 06-2: Reimplement and
Exercise 06-3: Reimplement concat
Exercise 06-4: Reimplement replicate
Exercise 06-5: Reimplement !! (0-based)
Exercise 06-6: Reimplement elem