anagram.hs

import Data.List (deleteFirstsBy, null)
import System.IO.UTF8 (readFile)

anagrams :: [Char] -> [String] -> [String]
anagrams [] _ = [""]
anagrams _ [] = []
anagrams letters dictionary = 
        let currentWord = head dictionary
            remainingLetters = removeWord letters currentWord
            newDictionary = filterDictionary remainingLetters dictionary
            anagramsOfRemainingLetters = anagrams remainingLetters newDictionary
            anagramsWithoutCurrentWord = anagrams letters $ tail dictionary
        in (prependWord currentWord anagramsOfRemainingLetters) ++ anagramsWithoutCurrentWord

removeWord :: [Char] -> String -> [Char]
removeWord = deleteFirstsBy (==)

prependWord :: String -> [String] -> [String]
prependWord word = map (\x -> word ++ " " ++ x)

filterDictionary :: [Char] -> [String] -> [String]
filterDictionary letters = filter (\x -> null $ deleteFirstsBy (==) x letters)

main = do
    dictionary <- fmap lines (System.IO.UTF8.readFile "dict.txt")
    letters <- fmap (concat . words) getLine
    putStr $ unlines $ anagrams letters $ filterDictionary letters dictionary