-- takes the last element, shifts all other elements to the right and puts the last element first
shiftr :: [a] -> [a]
shiftr [] = []
shiftr [a] = [a]
shiftr [a,b] = [b,a]
shiftr [a,b,c] = [c,a,b]
shiftr [a,b,c,d] = [d,a,b,c]