Encoding.hs

{-# LANGUAGE ImplicitParams,ForeignFunctionInterface #-}
{- | This module provides a replacement for the normal (unicode unaware) IO functions of haskell.
     By using implicit parameters, it can be used almost as a drop-in replacement.
     For example, consider the following simple echo program:

     > main = do
     >   str <- getContents
     >   putStr str

     To make this program process UTF-8 data, change the program to:

     > {-# LANGUAGE ImplicitParams #-}
     >
     > import Prelude hiding (getContents,putStr)
     > import System.IO.Encoding
     > import Data.Encoding.UTF8
     >
     > main = do
     >   let ?enc = UTF8
     >   str <- getContents
     >   putStr str

     Or, if you want to use the standard system encoding:

     > {-# LANGUAGE ImplicitParams #-}
     >
     > import Prelude hiding (getContents,putStr)
     > import System.IO.Encoding
     >
     > main = do
     >   e <- getSystemEncoding
     >   let ?enc = e
     >   str <- getContents
     >   putStr str     
 -}
module System.IO.Encoding
    (getSystemEncoding
    ,getContents
    ,putStr
    ,putStrLn
    ,hPutStr
    ,hPutStrLn
    ,hGetContents
    ,readFile
    ,writeFile
    ,appendFile
    ,getChar
    ,hGetChar
    ,getLine
    ,hGetLine
    ,putChar
    ,hPutChar
    ,interact
    ,print
    ,hPrint) where

import Foreign.C.String

import Data.Encoding
import System.IO (Handle,stdout,stdin)
import Prelude hiding (print,getContents,readFile,writeFile,appendFile,interact,putStr,putStrLn,getChar,getLine,putChar)
import qualified Data.ByteString.Lazy as LBS
import qualified Data.ByteString as BS
import Control.Monad.Reader (runReaderT)

-- | Like the normal 'System.IO.hGetContents', but decodes the input using an
--   encoding.
hGetContents :: (Encoding e,?enc :: e) => Handle -> IO String
hGetContents h = do
	str <- LBS.hGetContents h
	return $ decodeLazyByteString ?enc str

getContents :: (Encoding e,?enc :: e) => IO String
getContents = do
    str <- LBS.getContents
    return $ decodeLazyByteString ?enc str

putStr :: (Encoding e,?enc :: e) => String -> IO ()
putStr = hPutStr stdout

putStrLn :: (Encoding e,?enc :: e) => String -> IO ()
putStrLn = hPutStrLn stdout

-- | Like the normal 'System.IO.hPutStr', but encodes the output using an
--   encoding.
hPutStr :: (Encoding e,?enc :: e) => Handle -> String -> IO ()
hPutStr h str = LBS.hPut h (encodeLazyByteString ?enc str)

hPutStrLn :: (Encoding e,?enc :: e) => Handle -> String -> IO ()
hPutStrLn h str = do
    LBS.hPut h (encodeLazyByteString ?enc str)
    LBS.hPut h (encodeLazyByteString ?enc "\n")

print :: (Encoding e,Show a,?enc :: e) => a -> IO ()
print = hPrint stdout

hPrint :: (Encoding e,Show a,?enc :: e) => Handle -> a -> IO ()
hPrint h x = hPutStrLn h (show x)

readFile :: (Encoding e,?enc :: e) => FilePath -> IO String
readFile fn = LBS.readFile fn >>= return.(decodeLazyByteString ?enc)

writeFile :: (Encoding e,?enc :: e) => FilePath -> String -> IO ()
writeFile fn str = LBS.writeFile fn $ encodeLazyByteString ?enc str

appendFile :: (Encoding e,?enc :: e) => FilePath -> String -> IO ()
appendFile fn str = LBS.appendFile fn $ encodeLazyByteString ?enc str

getChar :: (Encoding e,?enc :: e) => IO Char
getChar = hGetChar stdin

hGetChar :: (Encoding e,?enc :: e) => Handle -> IO Char
hGetChar h = runReaderT (decodeChar ?enc) h

getLine :: (Encoding e,?enc :: e) => IO String
getLine = hGetLine stdin

hGetLine :: (Encoding e,?enc :: e) => Handle -> IO String
hGetLine h = do
  line <- BS.hGetLine h
  return $ decodeStrictByteString ?enc line

putChar :: (Encoding e,?enc :: e) => Char -> IO ()
putChar = hPutChar stdout

hPutChar :: (Encoding e,?enc :: e) => Handle -> Char -> IO ()
hPutChar h c = runReaderT (encodeChar ?enc c) h

interact :: (Encoding e,?enc :: e) => (String -> String) -> IO ()
interact f = do
  line <- hGetLine stdin
  hPutStrLn stdout (f line)

#ifdef SYSTEM_ENCODING
foreign import ccall "system_encoding.h get_system_encoding"
	get_system_encoding :: IO CString
#endif

-- | Returns the encoding used on the current system. Currently only supported
-- on Linux-alikes.
getSystemEncoding :: IO DynEncoding
getSystemEncoding = do
#ifdef SYSTEM_ENCODING
	enc <- get_system_encoding
	str <- peekCString enc
	return $ encodingFromString str
#else
	error "getSystemEncoding is not supported on this platform"
#endif