Oh, I am lost now - for now anyway. I am attempting to do next exercise in the book to define reverse function using primitive recursion and pattern matching on lists. But getting stack because when i con in front of xs (xs:x) i get en error, which i thought i would be getting anyway. I tried to define a helper function and cons there in front of xs and i get type errors again. I know these are easy and boring questions but i would appreciate a hint. Thank you Neil Mitchell wrote:
Hi
unique = unique' []
unique' _ [] = [] unique' history (x:xs) = if x `elem` history then next else (x:next) where next = (uniq' (x:hist) xs)
You can express this more neatly:
unique' _ [] = [] unique' history (x:xs) = [x | x `notElem` history] ++ unique' (x:history) xs
Thanks
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