# Anagrams

From HaskellWiki

Revision as of 11:08, 25 October 2006 by Ptolomy (talk | contribs) (updated to for 6.6.. minor cleanups.)

```
module Main (main) where
import System.Environment (getArgs)
import Data.Char (toUpper,isAlpha)
import Data.List (sortBy)
import Data.Ord (comparing)
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 = do
[n] <- getArgs
wl <- B.readFile n
user <- B.getLine
let results = findAnagrams (makeWordList wl) (countChars user)
B.putStr . B.unlines . map B.unwords $ results
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) = do rem <- xs `minus` r
return $! lft:rem
| (c1 == c2) && (i2 > i1) = fail "right has more chars than left"
| (c1 > c2) = fail "right has chars not in left"
| 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.head x) (B.length x)
makeWordList :: B.ByteString -> [WordData]
makeWordList = map (\w -> WordData w (countChars w)) . sortBy (flip (comparing B.length)) . B.words
```