Efficient locale-sensitive support for text I/O.
Skip past the synopsis for some important notes on performance and portability across different versions of GHC.
- readFile :: FilePath -> IO Text
- writeFile :: FilePath -> Text -> IO ()
- appendFile :: FilePath -> Text -> IO ()
- hGetContents :: Handle -> IO Text
- hGetLine :: Handle -> IO Text
- hPutStr :: Handle -> Text -> IO ()
- hPutStrLn :: Handle -> Text -> IO ()
- interact :: (Text -> Text) -> IO ()
- getContents :: IO Text
- getLine :: IO Text
- putStr :: Text -> IO ()
- putStrLn :: Text -> IO ()
The functions in this module obey the runtime system's locale, character set encoding, and line ending conversion settings.
If you know in advance that you will be working with data that has a specific encoding (e.g. UTF-8), and your application is highly performance sensitive, you may find that it is faster to perform I/O with bytestrings and to encode and decode yourself than to use the functions in this module.
Whether this will hold depends on the version of GHC you are using, the platform you are working on, the data you are working with, and the encodings you are using, so be sure to test for yourself.
Note: The behaviour of functions in this module depends on the version of GHC you are using.
Beginning with GHC 6.12, text I/O is performed using the system or handle's current locale and line ending conventions.
Under GHC 6.10 and earlier, the system I/O libraries do not support locale-sensitive I/O or line ending conversion. On these versions of GHC, functions in this library all use UTF-8. What does this mean in practice?
- All data that is read will be decoded as UTF-8.
- Before data is written, it is first encoded as UTF-8.
- On both reading and writing, the platform's native newline conversion is performed.
If you must use a non-UTF-8 locale on an older version of GHC, you will have to perform the transcoding yourself, e.g. as follows:
import qualified Data.ByteString as B import Data.Text (Text) import Data.Text.Encoding (encodeUtf16) putStr_Utf16LE :: Text -> IO () putStr_Utf16LE t = B.putStr (encodeUtf16LE t)
Write a string to a file. The file is truncated to zero length before writing begins.
Operations on handles
Internally, this function reads a chunk at a time from the lower-level buffering abstraction, and concatenates the chunks into a single string once the entire file has been read.
As a result, it requires approximately twice as much memory as its result to construct its result. For files more than a half of available RAM in size, this may result in memory exhaustion.
Special cases for standard input and output
interact function takes a function of type
Text -> Text
as its argument. The entire input from the standard input device is
passed to this function as its argument, and the resulting string
is output on the standard output device.