(**) Pack consecutive duplicates of list elements into sublists. If a list contains repeated elements they should be placed in separate sublists.
pack (x:xs) = let (first,rest) = span (==x) xs in (x:first) : pack rest pack  = 
A more verbose solution is
This is implemented as
pack :: Eq a => [a] -> [[a]] pack  =  pack (x:xs) = (x:first) : pack rest where getReps  = (, ) getReps (y:ys) | y == x = let (f,r) = getReps ys in (y:f, r) | otherwise = (, (y:ys)) (first,rest) = getReps xs