Hello, Habr.

So, the last time we empirically proved that you can quite easily write a kind of toy wc on the Haskell, which is significantly faster than the GNU Coreutils wc implementation. It’s clear that this is not a completely honest comparison: our program can do nothing but count bytes, strings and words, while the real wc is much more powerful: it has several more statistics, supports options, can read from stdin ... In short, we really it turned out just a toy.

Today we will fix it. Our main goal is to allow the user to select specific statistics for calculation, while not counting what the user does not need. And most importantly - we will strive for modularity, highlighting each statistic in a separate isolated unit.

Indeed, if we look at the C-version - well, personally, I would not call it a sample of readable and supported code, since everything happens there in one large function on 370 lines. We will try to avoid this.

The main function of the C-version did not fit on the 4k screen in portrait orientation with the 4th font.

In addition to this modularization, we, among other things:

• we express the idea that some statistics like counting the number of bytes can work more efficiently on the entire input, while others should look at each byte;
• we implement even more statistics, enjoying the opportunity to talk about each of them individually (what is called local reasoning);
• we’ll write some tests, enjoying local reasoning once again;
• we’ll try some almost-dependently typed techniques, having successfully received correctly working, but enchantingly braking code;
• Template Haskell;
• () () .

, :

{-# LANGUAGE Strict #-}
{-# LANGUAGE RecordWildCards #-}

module Data.WordCount where

import qualified Data.ByteString.Lazy as BS

data State = State
  { bs :: Int
  , ws :: Int
  , ls :: Int
  , wasSpace :: Int
  }

wc :: BS.ByteString -> (Int, Int, Int)
wc s = (bs, ws + 1 - wasSpace, ls)
  where
    State { .. } = BS.foldl' go (State 0 0 0 1) s

    go State { .. } c = State (bs + 1) (ws + addWord) (ls + addLine) isSp
      where
        isSp | c == 32 || c - 9 <= 4 = 1
             | otherwise = 0
        addLine | c == 10 = 1
                | otherwise = 0
        addWord = (1 - wasSpace) * isSp
{-# INLINE wc #-}

, , . ?

, . , BS.foldl'!

foldl, «, ». , ! , , ByteString. , : ( , length ), count ( count 10). , , !

, , . :

{-# LANGUAGE Strict #-}

import qualified Control.Foldl as L
import qualified Data.ByteString as BS

data WordState = WordState { ws :: Int, wasSpace :: Int }

wordsCount :: L.Fold BS.ByteString Int
wordsCount = L.Fold (BS.foldl' go) (WordState 0 1) (\WordState { .. } -> ws + 1 - wasSpace)
  where
    go WordState { .. } c = WordState (ws + addWord) isSp
      where
        isSp | c == 32 || c - 9 <= 4 = 1
             | otherwise = 0
        addWord = (1 - wasSpace) * isSp

, :

import qualified Control.Foldl.ByteString as BL
import qualified Data.ByteString.Lazy as BSL

main :: IO ()
main = do
  [path] <- getArgs
  contents <- unsafeMMapFile path
  let res = BL.fold ((,,) <$> BL.length <*> BL.count 10 <*> wordsCount) (BSL.fromStrict contents) :: (Int, Int, Int)
  print res

! ?

, ( 1.8- , tmpfs- IO, ), 2.5 . , , , ( wc, ), IDE, .

, 2.5 . , .

, ?

  let res = BL.fold ((,) <$> BL.length <*> wordsCount) contents :: (Int, Int)
  print res

1.55 . . ?

  let res = BL.fold (BL.count 10) contents :: Int
  print res

1.05 .

. . ! , ( '\n') , .

. , , foldl.

foldl . . foldl ByteString', ByteString', . — 256 , L1-, L2 L1 ( L1 ).

, , 16-32 , L1, .

, , , , : BL.fold ((,) <$> wordsCount <*> wordsCount) contents ( , ) BL.fold wordsCount contents. .

, , « », , .

...

, , . - . ?

- «» ( , ) f1, f2, f3, f1 f3. , , ,

  -- options —   ,   
  options <- parseCliOptions

  -- theFold —  
  let theFold = foldl' f (zip options [f1, f2, f3]) emptyFold
  where
    f acc (True, stat) = acc `compose` stat
    f acc (False, _) = acc

, , .

, — . , , , .

?

— . , , , :

{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE MultiParamTypeClasses, UndecidableInstances, FlexibleInstances #-}
{-# LANGUAGE TypeFamilyDependencies, FunctionalDependencies, PolyKinds, DataKinds, GADTs, TypeOperators #-}
{-# LANGUAGE ScopedTypeVariables #-}

- ? :

• ,
• -, ,
• -,
• .

:

class Statistic s res st | res -> s, st -> s
                         , s -> res, s -> st
                         where
  initState :: st
  extractState :: st -> res
  step :: st -> Word8 -> st

s ( DataKinds), , , . , - :

  initState :: proxy1 s -> proxy2 res -> st
  extractState :: proxy s -> st -> res
  step :: proxy1 s -> proxy2 res -> st -> Word8 -> st

, , , .

, , , , .

, - . , , , . , , . , $$$O(n)$$$$O(1)$. , (, , ) «» ( SIMD-, ). , . , , .

, , , ? GADT! - , GADT , . :

data StatCompTyOf = Chunked | ByteOnly

data StatComputation st compTy where
  ChunkedComputation :: (st -> Word8 -> st)
                     -> (st -> BS.ByteString -> st)
                     -> StatComputation st 'Chunked
  ByteOnlyComputation :: (st -> Word8 -> st)
                      -> StatComputation st 'ByteOnly

( ) BS — , .

Statistic, comp step computation:

class Statistic s res st comp | res -> s, st -> s
                              , s -> res, s -> st, s -> comp
                              where
  initState :: st
  extractState :: st -> res
  computation :: StatComputation st comp

. s, res, st, .

, , . , SIMD- , 16-32 . .

? :

• ,
• (UTF-8)-,
• ,
• ,
• .

:

data Statistics = Bytes | Chars | Words | MaxLL | Lines deriving (Eq, Ord)

, wc .

— Statistic. , — , :

newtype Tagged a = Tagged Word64 deriving (Eq, Show, Num)

a , Tagged 'Bytes Tagged 'Chars.

: :

instance Statistic 'Bytes (Tagged 'Bytes) (Tagged 'Bytes) 'Chunked where
  initState = 0
  extractState = id
  computation = ChunkedComputation (\st _ -> st + 1) (\st str -> st + fromIntegral (BS.length str))

, , :

1. , Bytes , Tagged 'Bytes , . , .
2. ( , ) 0.
3. , , — .
4. computation , 'Chunked . , .

.

, , ,

instance Statistic 'Lines (Tagged 'Lines) (Tagged 'Lines) 'Chunked where
  initState = 0
  extractState = id
  computation = ChunkedComputation (\st c -> st + if c == 10 then 1 else 0) (\st str -> st + fromIntegral (BS.count 10 str))

data WordsState = WordsState { ws :: Word64, wasSpace :: Word64 }

instance Statistic 'Words (Tagged 'Words) WordsState 'ByteOnly where
  initState = WordsState 0 1
  extractState WordsState { .. } = Tagged (ws + 1 - wasSpace)
  computation = ByteOnlyComputation step
    where
      step WordsState { .. } c = WordsState (ws + (1 - wasSpace) * isSp) isSp
        where
          isSp | c == 32 || c - 9 <= 4 = 1
               | otherwise = 0

instance Statistic 'Chars (Tagged 'Chars) (Tagged 'Chars) 'ByteOnly where
  initState = 0
  extractState = id
  computation = ByteOnlyComputation $ \cnt c ->
        cnt + 1 - fromIntegral (   ((c .&. 0b10000000) `shiftR` 7)
                               .&. (1 - ((c .&. 0b01000000) `shiftR` 6))
                               )

instance Statistic 'MaxLL (Tagged 'MaxLL) MaxLLState 'ByteOnly where
  initState = MaxLLState 0 0
  extractState MaxLLState { .. } = Tagged $ max maxLen curLen
  computation = ByteOnlyComputation step
    where
      step MaxLLState { .. } 9 = MaxLLState maxLen $ curLen + 8 - (curLen `rem` 8)
      step MaxLLState { .. } 8 = MaxLLState maxLen $ max 0 (curLen - 1)
      step MaxLLState { .. } c | c == 10
                              || c == 12
                              || c == 13 = MaxLLState (max maxLen curLen) 0
                               | c < 32 = MaxLLState maxLen curLen
      step MaxLLState { .. } _ = MaxLLState maxLen (curLen + 1)

, . : .

a — , b — , — , . :

infixr 5 :::
data a ::: b = a ::: b deriving (Show)

(,), , , , , .

, .

-, ? , , . :

type family CombineCompTy a b where
  CombineCompTy 'Chunked 'Chunked = 'Chunked
  CombineCompTy _ _ = 'ByteOnly

Statistic ? - :

instance (Statistic sa resa sta compa, Statistic sb resb stb compb)
       => Statistic (sa '::: sb) (resa ::: resb) (sta ::: stb) (CombineCompTy compa compb) where
  initState = initState ::: initState
  extractState (a ::: b) = extractState a ::: extractState b
  computation =
    case (computation :: StatComputation sta compa, computation :: StatComputation stb compb) of
         (ByteOnlyComputation a, ChunkedComputation b _)
            -> ByteOnlyComputation $ combine a b
         (ChunkedComputation a _, ByteOnlyComputation b)
            -> ByteOnlyComputation $ combine a b
         (ByteOnlyComputation a, ByteOnlyComputation b) 
            -> ByteOnlyComputation $ combine a b
         (ChunkedComputation stepA chunkA, ChunkedComputation stepB chunkB)
            -> ChunkedComputation (combine stepA stepB) (combine chunkA chunkB)
    where
      combine fa fb = \(a ::: b) w -> fa a w ::: fb b w

, sa — resa, sta compa, sb/resb/stb/compb, sa ::: sb — , — resa ::: resb, — sta ::: stb, — CombineCompTy compa compb.

( , ) :::--- ( , ) :::--- . sa sb — , , () , — , () .

, … . . , comp , :

instance (Statistic sa resa sta compa,
          Statistic sb resb stb compb,
          comp ~ CombineCompTy compa compb)
       => Statistic (sa '::: sb) (resa ::: resb) (sta ::: stb) comp where

.

. :

1. .
2. , - .

, — , !

, CombineCompTy ( ). , , ( ), .

- , , , , , case .

? , StatComputation st comp, , , comp ~ CombineCompTy compa compb. , compa compb. CombineCompTy, , Chunked compa, compb, .

compa compb? . , computation, GADT. , StatComputation. ChunkedComputation, comp Chunked. ByteOnlyComputation, ByteOnly.

, CombineCompTy _-, , compa, compb.

, : Words '::: Words , . ⊤ , , , .

, . ?

, Statistic, ByteString, . GADT, computation. ChunkedComputation, . ByteOnlyComputation, BS.foldl'. :

wc :: forall s res st comp. Statistic s res st comp => BS.ByteString -> res
wc s = extractState $! runCompute computation
  where
    runCompute :: StatComputation st comp -> st
    runCompute (ByteOnlyComputation step) = BS.foldl' step initState s
    runCompute (ChunkedComputation _ chunker) = chunker initState s

, (s, st, comp) res. , , runCompute, . st comp wc, ( ) forall ScopedTypeVariables.

:

let result = wc someBS :: Tagged 'Words ::: Tagged 'Lines

TypeApplications s :

let result = wc @('Words '::: 'Lines) someBS

, , , , .

, ?

, wc @'Words, . — 1.51 , , , . , .

? wc @('Words '::: 'Words)!

. , , , — , … : 1.34 . wc @('Words '::: 'Words '::: 'Words)? 1.30 . , 'Words .

— . #haskell — . .

. GHC Core — , . , , , - . , … -. , , , .

, , . , ? wc @('Bytes '::: 'Words '::: 'Lines)! — 1.53 . 1.45 , , , , .

, , . , .

— ! , .

, , , words, 127. , , .

QuickCheck-, ASCII, UTF-8-:

import qualified Data.ByteString.Char8 as BS
import qualified Data.Text as T
import qualified Data.Text.Encoding as T
--   

import Data.WordCount

wrapUnicode :: UnicodeString -> (BS.ByteString, T.Text)
wrapUnicode ustr = (T.encodeUtf8 txt, txt)
  where
    txt = T.pack $ getUnicodeString ustr

replaceNonAsciiSpaces :: Char -> Char
replaceNonAsciiSpaces ch | ch >= chr 127 && isSpace ch = '_'
                         | otherwise = ch

main :: IO ()
main = hspec $ parallel $ modifyMaxSuccess (const 10000) $ modifyMaxSize (const 1000) $ do
  describe "ASCII support" $ do
    it "Counts bytes correctly" $ property $
      \(getASCIIString -> str) -> wc @'Bytes (BS.pack str) `shouldBe` genericLength str
    it "Counts chars correctly" $ property $
      \(getASCIIString -> str) -> wc @'Chars (BS.pack str) `shouldBe` genericLength str
    it "Counts words correctly" $ property $
      \(getASCIIString -> str) -> wc @'Words (BS.pack str) `shouldBe` genericLength (words str)
    it "Counts lines correctly" $ property $
      \(getASCIIString -> str) -> wc @'Lines (BS.pack str) `shouldBe` genericLength (filter (== '\n') str)
  describe "UTF8 support" $ do
    it "Counts bytes correctly" $ property $
      \(wrapUnicode -> (bs, _))   -> wc @'Bytes bs `shouldBe` fromIntegral (BS.length bs)
    it "Counts chars correctly" $ property $
      \(wrapUnicode -> (bs, txt)) -> wc @'Chars bs `shouldBe` fromIntegral (T.length txt)
    it "Counts words correctly" $ property $
      \(wrapUnicode -> (bs, txt)) -> wc @'Words bs `shouldBe` genericLength (T.words $ T.map replaceNonAsciiSpaces txt)
    it "Counts lines correctly" $ property $
      \(wrapUnicode -> (bs, txt)) -> wc @'Lines bs `shouldBe` fromIntegral (T.count "\n" txt)

!

:

• , , . , - UTF-8- .
• , … .
• : 10 ( ) 3-5 ( ).

, - C GNU Coreutils.

optparse-applicative. , , :

data Options = Options
  { countBytes :: Bool
  , countChars :: Bool
  , countLines :: Bool
  , countMaxLineLength :: Bool
  , countWords :: Bool
  , files :: [FilePath]
  }

options :: Parser Options
options = Options
  <$> switch (long "bytes" <> short 'c' <> help "print the byte counts")
  <*> switch (long "chars" <> short 'm' <> help "print the character counts")
  <*> switch (long "lines" <> short 'l' <> help "print the newline counts")
  <*> switch (long "max-line-length" <> short 'L' <> help "print the maximum display width")
  <*> switch (long "words" <> short 'w' <> help "print the word counts")
  <*> some (argument str (metavar "FILES..."))

main, Statistics, , :

main :: IO ()
main = do
  Options { .. } <- execParser $ info (options <**> helper) (fullDesc <> progDesc "Print newline, word, and byte counts for each file")
  let selectedStats = map snd $ filter fst [ (countBytes, Bytes), (countChars, Chars)
                                           , (countWords, Words), (countMaxLineLength, MaxLL)
                                           , (countLines, Lines)
                                           ]
  let stats | null selectedStats = [Bytes, Words, Lines]
            | otherwise = selectedStats

, , - .

, . ? , wc. , , . !

, , , , - , — !

, , , .

, , :

data SomeStats where
  MkSomeStats :: Statistic s res st comp => proxy s -> SomeStats

proxy s — Statistic. — .

. ? - :

wc' :: SomeStats -> BS.ByteString -> ?
wc' (MkSomeStats (_ :: proxy s)) input = wc @s input

… ?? ? , res Statistic, .

, - ?

data SomeStats where
  MkSomeStats :: Statistic s res st comp => proxy1 s -> proxy2 res -> SomeStats

wc' :: SomeStats -> BS.ByteString -> res
wc' (MkSomeStats (_ :: proxy1 s) (_ :: proxy2 res)) input = wc @s input

, : wc' res, SomeStats, .

?

. wc, ! , . , , , , show, , res Show:

data SomeStats where
  MkSomeStats :: (Statistic s res st comp, Show res) => proxy s -> SomeStats

wc :

wc' :: SomeStats -> BS.ByteString -> String
wc' (MkSomeStats (_ :: proxy s)) input = show $ wc @s input

.

, stats SomeStats? :

promoteStat :: Statistics -> SomeStats
promoteStat Bytes = MkSomeStats (Proxy :: Proxy 'Bytes)
promoteStat Chars = MkSomeStats (Proxy :: Proxy 'Chars)
promoteStat Words = MkSomeStats (Proxy :: Proxy 'Words)
promoteStat MaxLL = MkSomeStats (Proxy :: Proxy 'MaxLL)
promoteStat Lines = MkSomeStats (Proxy :: Proxy 'Lines)

, , Statistics, . - : , Bytes () 'Bytes , , .

, promoteStat :

promoteStats :: [Statistics] -> SomeStats
promoteStats [s] = promoteStat s
promoteStats (s:ss) =
  case (promoteStat s, promoteStats ss) of
       (MkSomeStats (_ :: proxy1 st), MkSomeStats (_ :: proxy2 sst))
                                   -> MkSomeStats (Proxy :: Proxy (st '::: sst))

, , promoteStat.

, . : promoteStat, promoteStats. - , . promoteStat promoteStats, st , , sst — , .

, Statistic ( ). Statistic, st ::: sst Statistic - , ! , , rest resst ( , st sst) Show. , rest ::: resst Show, st ::: sst!

, , MkSomeStats (Proxy :: Proxy (st '::: sst)) . , !

, : . , , NonEmpty .

, :

main :: IO ()
main = do
  -- obtaining `stats` as before
  forM_ files $ \path -> do
    contents <- unsafeMMapFile path
    putStrLn $ wc' (promoteStats stats) contents

() ?

, 1.05 — , BS.count 10.

, . , , ? , … 14 .

, 14 .

, , :

  74,873,139,008 bytes allocated in the heap

, . , $$$O(1)$— GC (60,512 bytes maximum residency).

. , , ? 27 , 120 .

, ? ?

«42 », : 41 194 . , RTS 60 .

?

, :

wc' (MkSomeStats (_ :: proxy s)) input = show $ wc @s input

, computation s — -, , . , Statistic .

?

wc' computation, SomeStats wc, . , , , . , 1.8 — !

promoteStats. ?

, stats ,

promoteStats [s] = promoteStat s

s , , Words, promoteStat

promoteStat Words = MkSomeStats (Proxy :: Proxy 'Words)

promoteStats SomeStats , Statistic Words.

. , ?

promoteStats (s:ss) =
  case (promoteStat s, promoteStats ss) of
         (MkSomeStats (_ :: proxy1 st), MkSomeStats (_ :: proxy2 sst)) -> MkSomeStats (Proxy :: Proxy (st '::: sst))

computation : case , promoteStat promoteStats, , , computation Statistic «» sa ::: sb, , , .

, 13-14 , 28 — . , 65-70 .

, ( ) .

, . 13 (14 1 -) 1.8 — , 7 . .

: , () wc . -

main = do
  -- ..
  case stats of
       [Words] -> print $ wc @'Words contents
       [Bytes] -> print $ wc @'Bytes contents
       [Lines] -> print $ wc @'Lines contents
       [Words, Bytes] -> print $ wc @('Words '::: 'Bytes) contents
       [Lines, Bytes] -> print $ wc @('Lines '::: 'Bytes) contents
       -- ...

. , , $$$2^5 - 1 = 31$case. , — .

, Template Haskell. (-) dispatch, :

  contents <- unsafeMMapFile path
  putStrLn $ $(dispatch 'wc 'contents) stats

$(dispatch 'wc 'contents) , case- stats , .

dispatch — Template Haskell, , :

dispatch :: Name -> Name -> Q Exp
dispatch fun bs = reify ''Statistics >>= \case
  TyConI (DataD _ _ _ _ cons _) -> do
    let consNames = [ name | NormalC name _ <- cons ]
    let powerset = filterM (const [True, False]) consNames
    let matches = buildMatch fun bs <$> filter (not . null) powerset
    fallbackMatch <- (\body -> Match WildP (NormalB body) []) <$> [e| error "Unexpected input" |]
    pure $ LamCaseE $ matches <> [fallbackMatch]
  _ -> fail "unsupported type"

buildMatch :: Name -> Name -> [Name] -> Match
buildMatch fun bs consNames = Match (ListP $ (`ConP` []) <$> consNames) (NormalB $ VarE 'show `AppE` (wcCall `AppE` VarE bs)) []
  where
    wcCall = VarE fun `AppTypeE` foldr1 f (PromotedT <$> consNames)
    f accTy promotedTy = PromotedT '(:::) `AppT` accTy `AppT` promotedTy

, Statistics (, , ), ( , powerset) case- buildMatch. -case ( {-# LANGUAGE LambdaCase #-}).

, , , , .

, (, TH) — , stats . . ,

  let selectedStats = map snd $ filter fst [ (countBytes, Bytes), (countChars, Chars)
                                           , (countWords, Words), (countMaxLineLength, MaxLL)
                                           , (countLines, Lines)
                                           ]

, Ord. , stats. , , - stats, , .

!

main :: IO ()
main = do
  Options { .. } <- execParser $ info (options <**> helper) (fullDesc <> progDesc "Print newline, word, and byte counts for each file")
  let selectedStats = map snd $ filter fst [ (countBytes, Bytes), (countChars, Chars)
                                           , (countWords, Words), (countMaxLineLength, MaxLL)
                                           , (countLines, Lines)
                                           ]
  let stats | null selectedStats = [Bytes, Words, Lines]
            | otherwise = selectedStats
  forM_ files $ \path -> do
    contents <- unsafeMMapFile path
    putStrLn $ $(dispatch 'wc 'contents) stats

? (31 — ), - . , wc GNU Coreutils , -. , : 5 1.8 , . wc Coreutils LC_ALL=C LANG=C, .

:

:

• , , .
• , C (, , ) , . .
• ¹ , time 0.00user .
• ² (1.06 ) — bytestring. — bytestring, (count) SIMD-. count C, , , , ( , SIMD), .
• ³ wc UTF-8-, , , , UTF-8-.

, .

, , wc, . ?

: forM_ forConcurrently_ async:

main :: IO ()
main = do
  Options { .. } <- execParser $ info (options <**> helper) (fullDesc <> progDesc "Print newline, word, and byte counts for each file")
  let selectedStats = map snd $ filter fst [ (countBytes, Bytes), (countChars, Chars)
                                           , (countWords, Words), (countMaxLineLength, MaxLL)
                                           , (countLines, Lines)
                                           ]
  let stats | null selectedStats = [Bytes, Words, Lines]
            | otherwise = selectedStats
  forConcurrently_ files $ \path -> do
    contents <- unsafeMMapFile path
    putStrLn $ $(dispatch 'wc 'contents) stats

, (, RTS, ). , -j, .

?

1.22 — , .

, ( ), 1.47 , . , .

,

Tagged 123 ::: (Tagged 456 ::: Tagged 789)

, ! Statistic:

class Statistic s res st comp | res -> s, st -> s
                              , s -> res, s -> st, s -> comp where
  -- ...
  prettyPrint :: res -> String

, :

instance Statistic 'Bytes (Tagged 'Bytes) (Tagged 'Bytes) 'Chunked where
  -- ...
  prettyPrint (Tagged n) = show n <> " bytes"

, :

  prettyPrint (a ::: b) = prettyPrint a <> "\n" <> prettyPrint b

buildMatch, prettyPrint show:

buildMatch fun bs consNames = Match (ListP $ (`ConP` []) <$> consNames) (NormalB $ VarE 'prettyPrint `AppE` (wcCall `AppE` VarE bs)) []

!

, mmap. , : , hwc <(cat foo | grep bar).

, , — - mmap . mmap . ByteString, . ByteString — , :

import qualified Data.ByteString.Lazy as BSL

wcLazy :: forall s res st comp. Statistic s res st comp => BSL.ByteString -> res
wcLazy s = extractState $! runCompute computation
  where
    runCompute :: StatComputation st comp -> st
    runCompute (ByteOnlyComputation step) = BSL.foldl' step initState s
    runCompute (ChunkedComputation _ chunker) = BSL.foldlChunks chunker initState s

main:

  forConcurrently_ files $ \path -> do
    stat <- getFileStatus path
    if isRegularFile stat || isSymbolicLink stat
      then countStrict stats $ unsafeMMapFile path
      else countLazy stats $ BSL.readFile path

:

  where
    countStrict stats act = do
      contents <- act
      putStrLn $ $(dispatch 'wc 'contents) stats
    countLazy stats act = do
      contents <- act
      putStrLn $ $(dispatch 'wcLazy 'contents) stats

!

, wcLazy , , , .

stdin

, Coreutils wc, — stdin. , main:

main = do
  -- ... as before ...

  when (null files) $ countLazy stats BSL.getContents

-

cat testfile.txt | /usr/bin/time hwc-exe -cw

? , , 1.40 — , 1.22 .

, - : ? , , !

« » ( - ), stack build 7.9 , 2.24 ( strip).

Template Haskell : 23 . , ( 31 ): 2.34 , — 4.3%.

… stack build ( ). stack build --fast .

« » 5.6 --fast, TH … 7.8 . . .

, , C. , : wc GNU Coreutils 0.06 , — 21 . wc 24 . 100 , !

, , .

? , wc , Unix-, -wc , GNU Coreutils wc. — ( !), , , , . , - « , », C C++, C.

, :

1. wc , , , ;
2. ;
3. , , ;
4. , , , , , ;
5. Template Haskell;
6. , , ;
7. , .

.

, :

1. . , , , 16-32 ( L1). , 7 , 1.8 0.4 , 0.04%. Template Haskell!
2. Our implementation is still not the full equivalent wc, it does something differently. For example, character count statistics do not support encodings other than UTF-8 or ASCII, while it wcworks with an arbitrary locale, delegating all the work of processing glibc characters. But since our implementation makes it very easy to add new statistics, it’s quite simple to add support for something like that, and most importantly, it will not affect, say, the count of the number of lines or words. But about "do not pay for what you do not use," I already wrote a little higher.