haskell - Exception: Non-exhaustive patterns in function -


attempting create function removes duplicates list, , replaces them single element. keep getting error message "non-exhaustive patterns in function removeduplicate". assume means pattern matching missing possible case? think i've covered possibilities though. i'm new haskell, appreciated. 

removeduplicate :: (eq a) => [a] -> [a] removeduplicate [] = [] removeduplicate (x:[]) = [x] removeduplicate (x:z:[]) = if z == x [x] else (x:z:[]) removeduplicate (x:y:[xs])     | x == y = x:(removeduplicate [xs])     | otherwise = x:y:(removeduplicate [xs])

your problem in final pattern. assume meant match lists, way have it, matching list 1 element, xs, in it.

this means compiler seeing match 3 element list, not arbitrary length list, why complaining.

to fix this, remove box around xs.

removeduplicate (x:y:xs)     | x == y = x:(removeduplicate xs)     | otherwise = x:y:(removeduplicate xs)

now xs treated list, matching lists at least 3 items, rather 3 items.


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