The author suggests that Haskell could benefit from rewriting nodups = dedup [] where dedup m [] = m dedup m (x:xs) = dedup (if x `elem` m then

The author suggests that Haskell could benefit from rewriting nodups = dedup [] where dedup m [] = m dedup m (x:xs) = dedup (if x `elem` m then m else m++[x]) xs as some syntactic sugar while loop: nodups l = while k != [] k = l ||| tail l m = [] ||| if head k `elem` m then m else m ++ head k result = m but I would disagree. Btw, the former appears to suffer from quadratic slowdown due to repeated use of ++ which can be avoided by replacing m++[x] with x:m and making dedup m [] = reverse m.