enumerator-wc.hs

{-# LANGUAGE BangPatterns #-}

-----------------------------------------------------------------------------
-- |
-- Copyright: 2010 John Millikin
-- License: MIT
--
-- Maintainer: jmillikin@gmail.com
-- Portability: portable
--
-----------------------------------------------------------------------------
module Main (main) where
import qualified Control.Exception as Exc
import Data.Enumerator as E
import qualified Data.List as L
import qualified Data.Enumerator.Binary as EB
import qualified Data.Enumerator.Text as ET
import qualified Data.ByteString as B
import qualified Data.ByteString.Char8 as B8
import qualified Data.Text as T

-- support imports
import Control.Exception as E
import Data.List
import Control.Monad (unless, forM_)
import Control.Monad.Trans
import System.IO
import System.Console.GetOpt
import System.Environment
import System.Exit

-- support wc modes -c (bytes), -m (characters), and -l (lines)

-- iterBytes simply counts how many bytes are in each chunk, accumulates this
-- count, and returns it when EOF is received

iterBytes :: Monad m => Iteratee B.ByteString m Int
iterBytes = continue (step 0) where
    step acc EOF = yield acc EOF
    step acc (Chunks xs) = continue $ step $! Data.List.foldl' foldStep acc xs
    foldStep acc bytes = acc + (B.length bytes)

-- iterLines is similar, except it only counts newlines ('\n')
--
-- Because it's basically the same as 'iterBytes', we use it to demonstrate
-- the 'liftFoldL\'' helper function.

iterLines :: Monad m => Iteratee B.ByteString m Int
iterLines = E.continue (k 0)
  where
    k !acc EOF = return acc
    k !acc (Chunks xs) = let !nls = L.foldl' f 0 xs + acc in
                         E.continue (k nls)

    f !acc !bs = let !x = acc + B8.count '\n' bs in x


-- iterChars is a bit more complicated. It has to decode the input (for now,
-- assuming UTF-8) before performing any counting. Leftover bytes, not part
-- of a valid UTF-8 character, are yielded as surplus
--
-- Note the use of joinI. 'ET.decode' is an enumeratee, which means it returns
-- an iteratee yielding an inner step. 'joinI' "collapses" an enumeratee's
-- return value, much as 'join' does to monadic values.

iterChars :: Monad m => Iteratee B.ByteString m Int
iterChars = joinI (ET.decode ET.utf8 $$ count) where
    count = E.foldl' (\acc t -> acc + (T.length t)) 0


enumFile2 :: FilePath -> Enumerator B.ByteString IO b
enumFile2 path = enum
  where
    tryStep get io = do
        tried <- liftIO (Exc.try get)
        case tried of
            Right t -> io t
            Left err -> throwError (err :: Exc.SomeException)

    withHandle = tryStep (openBinaryFile path ReadMode)

    enum step = withHandle $ \h -> do
        Iteratee $ Exc.finally
            (runIteratee (EB.enumHandle (2^16) h step))
            (hClose h)


main :: IO ()
main = do
    (mode, files) <- getMode
    
    -- Exactly matching wc's output is too annoying, so this example
    -- will just print one line per file, and support counting at most
    -- one statistic per run
    let iter = case mode of
                 OptionBytes -> iterBytes
                 OptionLines -> iterLines
                 OptionChars -> iterChars
    
    forM_ files $ \filename -> do
        putStr $ filename ++ ": "
        
        -- see cat.hs for commented implementation of 'Data.Enumerator.IO.enumFile'
        eitherStat <- run (enumFile2 filename $$ iter)
        putStrLn $ case eitherStat of
            Left err -> "ERROR: " ++ show err
            Right stat -> show stat

-- uninteresting option parsing follows

data Option
    = OptionBytes
    | OptionChars
    | OptionLines

optionInfo :: [OptDescr Option]
optionInfo =
    [ Option ['c'] ["bytes"] (NoArg OptionBytes) "count bytes"
    , Option ['m'] ["chars"] (NoArg OptionChars) "count characters"
    , Option ['l'] ["lines"] (NoArg OptionLines) "count lines"
    ]

usage :: String -> String
usage name = "Usage: " ++ name ++ " <MODE> [FILES]"

getMode :: IO (Option, [FilePath])
getMode = do
    args <- getArgs
    let (options, files, errors) = getOpt Permute optionInfo args
    unless (null errors && not (null options) && not (null files)) $ do
        name <- getProgName
        hPutStrLn stderr $ concat errors
        hPutStrLn stderr $ usageInfo (usage name) optionInfo
        exitFailure
    
    return (Prelude.head options, files)