code: function last(foldable) {
      //  Fast path for arrays.
      if (Array.isArray (foldable)) {
        return foldable.length > 0 ? Just (foldable[foldable.length - 1])
                                   : Nothing;
      }
      return Z.reduce (function(_, x) { return Just (x); }, Nothing, foldable);
    }
docs: # last :: Foldable f => f a -> Maybe a . . Returns Just the last element of the given structure if the structure . contains at least one element; Nothing otherwise. . . ```javascript . > S.last ([1, 2, 3]) . Just (3) . . > S.last ([]) . Nothing . . > S.last (Cons (1) (Cons (2) (Cons (3) (Nil)))) . Just (3) . . > S.last (Nil) . Nothing . ```