Counting occurrences in a list

countOccurr.hs

import Data.List

count :: (Eq a, Ord a) => [a] -> [(a, Int)]
count = map wrap . group . sort
            where wrap g = (head g, length g)


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increment :: (Eq a) => [(a, Int)] -> a -> [(a, Int)]
increment counts elt | lookup elt counts == Nothing = (elt, 1) : counts
                     | otherwise = map incIfTarget counts
                        where incIfTarget (x, count) | x == elt = (x, count + 1)
                                                     | otherwise = (x, count)

count :: (Eq a) => [a] -> [(a, Int)]
count = foldl increment []