[Haskell-cafe] Most elegant funciton for removing adjacent
duplicates from a list using foldl and foldr
rj248842 at hotmail.com
Sun Mar 15 08:21:14 EDT 2009
I need to write an implementation using foldl, and a separate implementation using foldr, of a function, "remdups xs", that removes adjacent duplicate items from the list xs. For example, remdups [1,2,2,3,3,3,1,1]= [1,2,3,1].
My approach is first to write a direct recursion, as follows:
remdups :: (Eq a) => [a] -> [a]
remdups  = 
remdups (x : ) = [x]
remdups (x : xx : xs) = if x == xx then remdups (x : xs) else x : remdups (xx : xs)
This code works, but it has three cases, not usual two, namely  and (x : xs).
What, if any, is the implementation using only two cases?
Also, if three cases are required, then how can it be implemented using foldr, and how using foldl?
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