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Я пытаюсь выполнить сжатие LZW в Haskell с помощью монады, вот мой код до сих пор с тестами:LZW рутина в Haskell, используя Монады
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE FlexibleContexts #-}
import Control.Monad.State
import Control.Monad.Writer
import Data.Char (chr, ord)
import Data.List (isPrefixOf, maximumBy)
import Data.Function
import Test.QuickCheck
type Dictionary = [String]
dictionary :: Dictionary
dictionary = [[chr x] | x <- [0..127]]
test_dictionary =
[ map ord (concat dictionary) == [0..127]
, all (\str -> length str == 1) dictionary
]
prefixes :: String -> Dictionary -> [(Int, String)]
prefixes str dict = [(x, dict!!x) | x <- [0..length dict - 1], isPrefixOf (dict!!x) str]
test_prefixes =
[ prefixes "" dictionary == []
, prefixes "almafa" [] == []
, prefixes "almafa" ["al", "alma", "fa", "korte"] == [(0, "al"), (1, "alma")]
, prefixes "barack" dictionary == [(98, "b")]
]
longest :: [(Int, String)] -> (Int, String)
longest prefs = maximumBy (compare `on` (\(x,y) -> length y)) prefs
test_longest =
[ longest [(30, "a"), (20, "abc"), (15, "ab")] == (20, "abc")
, longest [(30, "a"), (20, "abc"), (15, "abc")] == (15, "abc")
]
instance MonadState Dictionary ((->) Dictionary) where
get = \s -> s
munch :: MonadState Dictionary m => String -> m (Int, String, String)
munch str = do
dict <- get
let longst = longest (prefixes str dict)
return (fst longst, snd longst, [str!!x | x <- [length (snd longst)..length str - 1]])
test_munch =
[ evalState (munch "a") ["a"] == (0, "a", "")
, evalState (munch "almafa") ["a"] == (0, "a", "lmafa")
, evalState (munch "barack") ["a", "ba", "b"] == (1, "ba", "rack")
]
instance MonadState m (StateT Dictionary ((->) m)) where
append :: MonadState Dictionary m => String -> String -> m()
append s "" = return()
append s w = do
dict <- get
let newWord = s ++ (take 1 w)
if (notElem newWord dict)
then do
put (dict++[newWord])
else return()
test_append =
[ execState (append "a" "") [] == []
, execState (append "a" "") dictionary == dictionary
, execState (append "a" "bc") [] == ["ab"]
, execState (append "a" "bc") ["ab"] == ["ab"]
]
encode :: String -> WriterT [Int] (State Dictionary)()
encode "" = return()
encode w = do
dict <- get
let (a, b, c) = (munch w) dict
if length dict < 256
then do
tell [a]
put ((append b c) dict)
encode c
else return()
test_encode =
[ evalState (execWriterT (encode "")) [] == []
, evalState (execWriterT (encode "aaa")) ["a"] == [0, 1]
, evalState (execWriterT (encode "aaaa")) ["a"] == [0, 1, 0]
, evalState (execWriterT (encode "aaaaa")) ["a"] == [0, 1, 1]
, evalState (execWriterT (encode "abababab")) ["a", "b"] == [0, 1, 2, 4, 1]
, evalState (execWriterT (encode "aaabbbccc")) dictionary
== [97, 128, 98, 130, 99, 132]
]
decode :: [Int] -> WriterT String (State Dictionary)()
decode [] = return()
decode [x] = do
dict <- get
tell (dict!!x)
decode (x:xs) = do
dict <- get
let f = dict!!x
let s = if(length dict > head xs)
then dict!!head xs
else f
tell f
put (append f s) dict
decode xs
test_decode =
[ evalState (execWriterT (decode [])) [] == []
, evalState (execWriterT (decode [0])) ["a"] == "a"
, evalState (execWriterT (decode [0, 1, 1, 0])) ["a", "b"] == "abba"
, evalState (execWriterT (decode [0, 1, 2, 0])) ["a", "b"] == "ababa"
, evalState (execWriterT (decode [0, 1, 2, 4, 1])) ["a", "b"] == "abababab"
, evalState (execWriterT (decode [97, 128, 98, 130, 99, 132])) dictionary
== "aaabbbccc"
]
compress :: String -> [Int]
compress w = evalState (execWriterT (encode w)) dictionary
test_compress =
[ compress "" == []
, compress "a" == [97]
, compress "aaa" == [97, 128]
, compress "aaabbbccc" == [97, 128, 98, 130, 99, 132]
]
decompress :: [Int] -> String
decompress list = evalState (execWriterT (decode list)) dictionary
test_decompress =
[ decompress [] == ""
, decompress [97] == "a"
, decompress [97, 128] == "aaa"
, decompress [97, 128, 98, 130, 99, 132] == "aaabbbccc"
]
prop_compressDecompress :: String -> Bool
prop_compressDecompress w = do
let tmp = [chr (div (ord x) 2) | x <- w]
decompress (compress tmp) == tmp
compressFile :: FilePath -> FilePath -> IO()
compressFile source target = do
s <- readFile source
let compressed = compress s
let chars = [chr x | x <- compressed]
writeFile target chars
decompressFile :: FilePath -> FilePath -> IO()
decompressFile source target = do
s <- readFile source
let code = [ord x | x <- s]
let decompressed = decompress code
writeFile target decompressed
allTests = [test_dictionary, test_prefixes, test_longest, test_munch, test_append
,test_encode
--, test_decode, test_compress, test_decompress
]
main = do
--quickCheck prop_compressDecompress
print (allTests, and (concat allTests))
С помощью этого кода я получаю следующее сообщение об ошибке (имеется в виду использование положить в "закодировать" и "Decode" функции):
[email protected]: 13-80: 16 Нет экземпляра для (MonadState() (StateT словарь Data.Functor.Identity.Identity)), возникающих в результате использования пула
Я попытался определить этот экземпляр, но лучшее, что я смог достичь, - это ошибка «конфликты функциональных зависимостей между экземплярами экземпляра». Как я уже говорил, я этого не понимаю, и я понятия не имею, что делать. Я знаю, что есть более простые решения без Monads, но я должен их использовать, также типы функций не подлежат изменению.
Не могли бы вы мне помочь в том, что я здесь делаю неправильно?