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Task/Ordered-words/Haskell/ordered-words-1.hs

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+-- Words are read from the standard input.  We keep in memory only the current
+-- set of longest, ordered words.
+--
+-- Limitation: the locale's collation order is not take into consideration.
+
+isOrdered wws@(_:ws) = and $ zipWith (<=) wws ws
+
+keepLongest _ acc [] = acc
+keepLongest max acc (w:ws) =
+  let len = length w in
+  case compare len max of
+    LT -> keepLongest max acc ws
+    EQ -> keepLongest max (w:acc) ws
+    GT -> keepLongest len [w] ws
+
+longestOrderedWords = reverse . keepLongest 0 [] . filter isOrdered
+
+main = do
+  str <- getContents
+  let ws = longestOrderedWords $ words str
+  mapM_ putStrLn ws