source: anagram/trunk/anagram.hs @ 45

-- anagram.hs: Program to find the anagrams of a word in a word list

import Char
import System
import IO

-- Remove one occurrence of an element from a list
deleteOne e [] = []
deleteOne e (y:ys)
    | e == y    = ys
    | otherwise = y : deleteOne e ys

-- Test if the strings is an re-arrangements of each other
anagram []     [] = True
anagram []     ys = False
anagram xs     [] = False
anagram (x:xs) ys = elem x ys && anagram xs (deleteOne x ys)

printStrList = putStr . concat . map (++ "\n")

main = do
    args <- getArgs
    case args of
        [string,file]  -> do
            chars <- readFile file
            printStrList (filter (anagram string') (phrases chars))
                where string'   = filter isAlpha string
                      phrases c = map (filter isAlpha) (lines c)
        [string]    -> do
            chars <- getContents
            printStrList (filter (anagram string) (lines chars))
        _           -> do
            putStr "Usage: "
            getProgName >>= putStr
            putStrLn " WORD [FILE]"
            putStrLn "List anagrams of WORD from FILE or standard input."
            exitWith (ExitFailure 1)