# Anagrams

### From HaskellWiki

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## Revision as of 00:38, 8 October 2006

module Main (main) where import System.Environment (getArgs) import Data.Char (toUpper,isAlpha) import Data.List (sortBy) import Control.Monad (liftM) import qualified Data.ByteString.Char8 as B data CharCount = CharCount !Char !Int deriving (Show, Eq) data WordData = WordData B.ByteString [CharCount] deriving (Show, Eq) main :: IO () main = do n <- head `fmap` getArgs wl <- liftM makeWordList $ B.readFile n user <- liftM countChars B.getLine case (findAnagrams wl user) of [] -> print "No anagrams." x -> B.putStr . B.unlines . map B.unwords $ x findAnagrams :: [WordData] -> [CharCount] -> [[B.ByteString]] findAnagrams [] _ = [] findAnagrams lst@((WordData bs cc):rest) qcc = case (qcc `minus` cc) of Nothing -> remaining Just [] -> [bs]:remaining Just x -> map ((:) bs) (findAnagrams lst x) ++ remaining where remaining = findAnagrams rest qcc minus :: (Monad m) => [CharCount] -> [CharCount] -> m [CharCount] minus x [] = return x minus [] _ = fail "can't subtract from empty" minus (lft@(CharCount c1 i1):xs) r@((CharCount c2 i2):ys) | (c1 == c2) && (i2 == i1) = xs `minus` ys | (c1 == c2) && (i2 < i1) = do rem <- xs `minus` ys return $! (CharCount c1 (i1 - i2)):rem | (c1 == c2) && (i2 > i1) = fail "right has more chars than left" | (c1 > c2) = fail "right has chars not in left" | (c1 < c2) = do rem <- xs `minus` r return $! lft:rem | otherwise = error "Bad condition" countChars :: B.ByteString -> [CharCount] countChars = map counts . B.group . B.sort . B.map toUpper . B.filter isAlpha where counts x = CharCount (B.unsafeHead x) (B.length x) makeWordList :: B.ByteString -> [WordData] makeWordList = map (\w -> WordData w (countChars w)) . sortBy bsLenCmp . B.words where bsLenCmp x y = compare (B.length y) (B.length x)