Problem 2 Solutions

Solution 1:

Recursive search for the last element

penultimate : List a -> Maybe a
penultimate list = 
  case list of
    [ ] -> Nothing
    [y] -> Nothing
    [y, z] -> Just y
    y::ys -> penultimate ys

Solution 2:

Reverse the list and take the head of the tail.

penultimate : List a -> Maybe a
penultimate list = 
  case List.reverse list of
    [ ] -> Nothing
    y::ys -> List.head ys

Solution 3:

Reverse the list, drop one and take the head.

penultimate : List a -> Maybe a
penultimate list = 
  case drop 1 (List.reverse list) of
    [ ] -> Nothing
    y::ys -> Just y

Back to Problem 2