poor soln h99 problems p28

p28.hs

import Data.List (elemIndex, sortBy, group, sort)
import Data.Ord (comparing)
import Data.Maybe (fromJust)

main = print demo
demo = lsort ["", "ab3","r3","fg3","d3","ijk1","mn","1", "abcdef1"]

lsort :: (Ord a) => [[a]] -> [[a]]
lsort xs = sortBy (comparing lfreq) xs
  where 
    lfreq ls = fromJust $ (length ls) `elemIndex` allLengths
    allLengths = map head $ sortBy (comparing length) $ group $ sort $ map length xs