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Spell corrector
import Data.Char (toLower)
import qualified Data.Map as Map -- (insertWith, empty, member)
import qualified Data.Set as Set -- (fromList, toList, union, unions)
main :: IO ()
main = do
fileStr <- readFile "big.txt"
let training = words $ toLower <$> fileStr
let knowledge = foldl (\m word -> Map.insertWith (+) word 1 m) Map.empty training
inputWord <- getLine
let candidates = Set.filter (`Map.member` knowledge) <$> [Set.fromList [inputWord], editOne inputWord, editTwo inputWord]
let realCand = head $ filter (not . Set.null) $ candidates ++ [Set.fromList [inputWord]]
-- print [(Map.findWithDefault 1 x knowledge, x) | x <- Set.toList realCand]
print $ snd $ maximum [(Map.findWithDefault 1 x knowledge, x) | x <- Set.toList realCand]
wordSplit word = take <$> [0..length word] <*> [word]
splits word = zip (wordSplit word) (reverse $ reverse <$> wordSplit (reverse word))
editDel word = [x ++ tail y | (x, y) <- splits word, not $ null y]
editTrans word = [x ++ [y!!1] ++ [head y] ++ drop 2 y | (x, y) <- splits word, length y > 1]
editReplace word = [x ++ [c] ++ y | (x, y) <- splits word, c <- ['a'..'z']]
editInsert word = [x ++ [c] ++ tail y | (x, y) <- splits word, c <- ['a'..'z'], not $ null y]
editOne word = Set.fromList $ concat $ [editDel, editTrans, editReplace, editInsert] <*> [word]
editTwo word = Set.unions $ editOne <$> Set.toList (editOne word)
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