text-0.7: An efficient packed Unicode text type





Efficient locale-sensitive support for text I/O.


Locale support

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)

readFile :: FilePath -> IO TextSource

The readFile function reads a file and returns the contents of the file as a string. The entire file is read strictly, as with getContents.

writeFile :: FilePath -> Text -> IO ()Source

Write a string to a file. The file is truncated to zero length before writing begins.

appendFile :: FilePath -> Text -> IO ()Source

Write a string the end of a file.

Operations on handles

hGetContents :: Handle -> IO TextSource

Read the remaining contents of a Handle as a string. The Handle is closed once the contents have been read, or if an exception is thrown.

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.

hGetLine :: Handle -> IO TextSource

Read a single line from a handle.

hPutStr :: Handle -> Text -> IO ()Source

Write a string to a handle.

hPutStrLn :: Handle -> Text -> IO ()Source

Write a string to a handle, followed by a newline.

Special cases for standard input and output

interact :: (Text -> Text) -> IO ()Source

The 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.

getContents :: IO TextSource

Read all user input on stdin as a single string.

getLine :: IO TextSource

Read a single line of user input from stdin.

putStr :: Text -> IO ()Source

Write a string to stdout.

putStrLn :: Text -> IO ()Source

Write a string to stdout, followed by a newline.