base-4.18.1.0: Basic libraries

Copyright | (c) The University of Glasgow 1994-2009
License | see libraries/base/LICENSE
Maintainer | libraries@haskell.org
Stability | internal
Portability | non-portable
Safe Haskell | Trustworthy
Language | Haskell2010

GHC.IO.Handle.Types

Description

Basic types for the implementation of IO Handles.

Synopsis

- data Handle
  - = FileHandle FilePath !(MVar Handle__)
  - | DuplexHandle FilePath !(MVar Handle__) !(MVar Handle__)
- data Handle__ = forall dev enc_state dec_state.(RawIO dev, IODevice dev, BufferedIO dev, Typeable dev) => Handle__ {
  - haDevice :: !dev
  - haType :: HandleType
  - haByteBuffer :: !(IORef (Buffer Word8))
  - haBufferMode :: BufferMode
  - haLastDecode :: !(IORef (dec_state, Buffer Word8))
  - haCharBuffer :: !(IORef (Buffer CharBufElem))
  - haBuffers :: !(IORef (BufferList CharBufElem))
  - haEncoder :: Maybe (TextEncoder enc_state)
  - haDecoder :: Maybe (TextDecoder dec_state)
  - haCodec :: Maybe TextEncoding
  - haInputNL :: Newline
  - haOutputNL :: Newline
  - haOtherSide :: Maybe (MVar Handle__)
  }
- showHandle :: FilePath -> String -> String
- checkHandleInvariants :: Handle__ -> IO ()
- data BufferList e
  - = BufferListNil
  - | BufferListCons (RawBuffer e) (BufferList e)
- data HandleType
  - = ClosedHandle
  - | SemiClosedHandle
  - | ReadHandle
  - | WriteHandle
  - | AppendHandle
  - | ReadWriteHandle
- isReadableHandleType :: HandleType -> Bool
- isWritableHandleType :: HandleType -> Bool
- isReadWriteHandleType :: HandleType -> Bool
- isAppendHandleType :: HandleType -> Bool
- data BufferMode
  - = NoBuffering
  - | LineBuffering
  - | BlockBuffering (Maybe Int)
- data BufferCodec from to state = BufferCodec {
  - encode :: CodeBuffer from to
  - recover :: Buffer from -> Buffer to -> IO (Buffer from, Buffer to)
  - close :: IO ()
  - getState :: IO state
  - setState :: state -> IO ()
  }
- data NewlineMode = NewlineMode {
  - inputNL :: Newline
  - outputNL :: Newline
  }
- data Newline
  - = LF
  - | CRLF
- nativeNewline :: Newline
- universalNewlineMode :: NewlineMode
- noNewlineTranslation :: NewlineMode
- nativeNewlineMode :: NewlineMode

# Documentation

data Handle Source #

Haskell defines operations to read and write characters from and to files, represented by values of type `Handle`. Each value of this type is a handle: a record used by the Haskell run-time system to manage I/O with file system objects. A handle has at least the following properties:

- whether it manages input or output or both;
- whether it is open, closed or semi-closed;
- whether the object is seekable;
- whether buffering is disabled, or enabled on a line or block basis;
- a buffer (whose length may be zero).

Most handles will also have a current I/O position indicating where the next input or output operation will occur. A handle is readable if it manages only input or both input and output; likewise, it is writable if it manages only output or both input and output. A handle is open when first allocated. Once it is closed it can no longer be used for either input or output, though an implementation cannot re-use its storage while references remain to it. Handles are in the `Show` and `Eq` classes. The string produced by showing a handle is system dependent; it should include enough information to identify the handle for debugging. A handle is equal according to `==` only to itself; no attempt is made to compare the internal state of different handles for equality.

Constructors

FileHandle FilePath !(MVar Handle__) |
DuplexHandle FilePath !(MVar Handle__) !(MVar Handle__) |

#### Instances

Instances details

Show Handle Source # | Since: base-4.1.0.0
Instance details Defined in GHC.IO.Handle.Types Methods showsPrec :: Int -> Handle -> ShowS Source # show :: Handle -> String Source # showList :: [Handle] -> ShowS Source #
Eq Handle Source # | Since: base-4.1.0.0
Instance details Defined in GHC.IO.Handle.Types Methods (==) :: Handle -> Handle -> Bool Source # (/=) :: Handle -> Handle -> Bool Source #

data Handle__ Source #

Constructors

forall dev enc_state dec_state.(RawIO dev, IODevice dev, BufferedIO dev, Typeable dev) => Handle__ |

Fields

- haDevice :: !dev
- haType :: HandleType
- haByteBuffer :: !(IORef (Buffer Word8))
- haBufferMode :: BufferMode
- haLastDecode :: !(IORef (dec_state, Buffer Word8))

  The byte buffer just before we did our last batch of decoding.

- haCharBuffer :: !(IORef (Buffer CharBufElem))
- haBuffers :: !(IORef (BufferList CharBufElem))
- haEncoder :: Maybe (TextEncoder enc_state)
- haDecoder :: Maybe (TextDecoder dec_state)
- haCodec :: Maybe TextEncoding
- haInputNL :: Newline
- haOutputNL :: Newline
- haOtherSide :: Maybe (MVar Handle__)

showHandle :: FilePath -> String -> String Source #

checkHandleInvariants :: Handle__ -> IO () Source #

data BufferList e Source #

Constructors

BufferListNil |
BufferListCons (RawBuffer e) (BufferList e) |

data HandleType Source #

Constructors

ClosedHandle |
SemiClosedHandle |
ReadHandle |
WriteHandle |
AppendHandle |
ReadWriteHandle |

#### Instances

Instances details

Show HandleType Source # | Since: base-4.1.0.0
Instance details Defined in GHC.IO.Handle.Types Methods showsPrec :: Int -> HandleType -> ShowS Source # show :: HandleType -> String Source # showList :: [HandleType] -> ShowS Source #

isReadableHandleType :: HandleType -> Bool Source #

isWritableHandleType :: HandleType -> Bool Source #

isReadWriteHandleType :: HandleType -> Bool Source #

isAppendHandleType :: HandleType -> Bool Source #

data BufferMode Source #

Three kinds of buffering are supported: line-buffering, block-buffering or no-buffering. These modes have the following effects. For output, items are written out, or flushed, from the internal buffer according to the buffer mode:

- line-buffering: the entire output buffer is flushed whenever a newline is output, the buffer overflows, a `hFlush` is issued, or the handle is closed.
- block-buffering: the entire buffer is written out whenever it overflows, a `hFlush` is issued, or the handle is closed.
- no-buffering: output is written immediately, and never stored in the buffer.

An implementation is free to flush the buffer more frequently, but not less frequently, than specified above. The output buffer is emptied as soon as it has been written out.

Similarly, input occurs according to the buffer mode for the handle:

- line-buffering: when the buffer for the handle is not empty, the next item is obtained from the buffer; otherwise, when the buffer is empty, characters up to and including the next newline character are read into the buffer. No characters are available until the newline character is available or the buffer is full.
- block-buffering: when the buffer for the handle becomes empty, the next block of data is read into the buffer.
- no-buffering: the next input item is read and returned. The `hLookAhead` operation implies that even a no-buffered handle may require a one-character buffer.

The default buffering mode when a handle is opened is implementation-dependent and may depend on the file system object which is attached to that handle. For most implementations, physical files will normally be block-buffered and terminals will normally be line-buffered.

Constructors

NoBuffering | buffering is disabled if possible.
LineBuffering | line-buffering should be enabled if possible.
BlockBuffering (Maybe Int) | block-buffering should be enabled if possible. The size of the buffer is `n` items if the argument is `Just` `n` and is otherwise implementation-dependent.

#### Instances

Instances details

Read BufferMode Source # | Since: base-4.2.0.0
Instance details Defined in GHC.IO.Handle.Types Methods readsPrec :: Int -> ReadS BufferMode Source # readList :: ReadS [BufferMode] Source # readPrec :: ReadPrec BufferMode Source # readListPrec :: ReadPrec [BufferMode] Source #
Show BufferMode Source # | Since: base-4.2.0.0
Instance details Defined in GHC.IO.Handle.Types Methods showsPrec :: Int -> BufferMode -> ShowS Source # show :: BufferMode -> String Source # showList :: [BufferMode] -> ShowS Source #
Eq BufferMode Source # | Since: base-4.2.0.0
Instance details Defined in GHC.IO.Handle.Types Methods (==) :: BufferMode -> BufferMode -> Bool Source # (/=) :: BufferMode -> BufferMode -> Bool Source #
Ord BufferMode Source # | Since: base-4.2.0.0

Instance details

Defined in GHC.IO.Handle.Types

Methods

compare :: BufferMode -> BufferMode -> Ordering Source #

(<) :: BufferMode -> BufferMode -> Bool Source #

(<=) :: BufferMode -> BufferMode -> Bool Source #

(>) :: BufferMode -> BufferMode -> Bool Source #

(>=) :: BufferMode -> BufferMode -> Bool Source #

max :: BufferMode -> BufferMode -> BufferMode Source #

min :: BufferMode -> BufferMode -> BufferMode Source #

data BufferCodec from to state Source #

Constructors

BufferCodec |

Fields

- encode :: CodeBuffer from to

  The `encode` function translates elements of the buffer `from` to the buffer `to`. It should translate as many elements as possible given the sizes of the buffers, including translating zero elements if there is either not enough room in `to`, or `from` does not contain a complete multibyte sequence.

  If multiple CodingProgress returns are possible, OutputUnderflow must be preferred to InvalidSequence. This allows GHC's IO library to assume that if we observe InvalidSequence there is at least a single element available in the output buffer.

  The fact that as many elements as possible are translated is used by the IO library in order to report translation errors at the point they actually occur, rather than when the buffer is translated.

- recover :: Buffer from -> Buffer to -> IO (Buffer from, Buffer to)

  The `recover` function is used to continue decoding in the presence of invalid or unrepresentable sequences. This includes both those detected by `encode` returning `InvalidSequence` and those that occur because the input byte sequence appears to be truncated.

  Progress will usually be made by skipping the first element of the `from` buffer. This function should only be called if you are certain that you wish to do this skipping and if the `to` buffer has at least one element of free space. Because this function deals with decoding failure, it assumes that the from buffer has at least one element.

  `recover` may raise an exception rather than skipping anything.

  Currently, some implementations of `recover` may mutate the input buffer. In particular, this feature is used to implement transliteration.

  Since: base-4.4.0.0

- close :: IO ()

  Resources associated with the encoding may now be released. The `encode` function may not be called again after calling `close`.

- getState :: IO state

  Return the current state of the codec.

  Many codecs are not stateful, and in these case the state can be represented as `()`. Other codecs maintain a state. For example, UTF-16 recognises a BOM (byte-order-mark) character at the beginning of the input, and remembers thereafter whether to use big-endian or little-endian mode. In this case, the state of the codec would include two pieces of information: whether we are at the beginning of the stream (the BOM only occurs at the beginning), and if not, whether to use the big or little-endian encoding.

- setState :: state -> IO ()

data NewlineMode Source #

Specifies the translation, if any, of newline characters between internal Strings and the external file or stream. Haskell Strings are assumed to represent newlines with the `'\n'` character; the newline mode specifies how to translate `'\n'` on output, and what to translate into `'\n'` on input.

Constructors

NewlineMode |

Fields

- inputNL :: Newline

  the representation of newlines on input

- outputNL :: Newline

  the representation of newlines on output

#### Instances

Instances details

Read NewlineMode Source # | Since: base-4.3.0.0
Instance details Defined in GHC.IO.Handle.Types Methods readsPrec :: Int -> ReadS NewlineMode Source # readList :: ReadS [NewlineMode] Source # readPrec :: ReadPrec NewlineMode Source # readListPrec :: ReadPrec [NewlineMode] Source #
Show NewlineMode Source # | Since: base-4.3.0.0
Instance details Defined in GHC.IO.Handle.Types Methods showsPrec :: Int -> NewlineMode -> ShowS Source # show :: NewlineMode -> String Source # showList :: [NewlineMode] -> ShowS Source #
Eq NewlineMode Source # | Since: base-4.2.0.0
Instance details Defined in GHC.IO.Handle.Types Methods (==) :: NewlineMode -> NewlineMode -> Bool Source # (/=) :: NewlineMode -> NewlineMode -> Bool Source #
Ord NewlineMode Source # | Since: base-4.3.0.0

Instance details

Defined in GHC.IO.Handle.Types

Methods

compare :: NewlineMode -> NewlineMode -> Ordering Source #

(<) :: NewlineMode -> NewlineMode -> Bool Source #

(<=) :: NewlineMode -> NewlineMode -> Bool Source #

(>) :: NewlineMode -> NewlineMode -> Bool Source #

(>=) :: NewlineMode -> NewlineMode -> Bool Source #

max :: NewlineMode -> NewlineMode -> NewlineMode Source #

min :: NewlineMode -> NewlineMode -> NewlineMode Source #

data Newline Source #

The representation of a newline in the external file or stream.

Constructors

LF

    '\n'

CRLF

    '\r\n'

#### Instances

Instances details

Read Newline Source # | Since: base-4.3.0.0
Instance details Defined in GHC.IO.Handle.Types Methods readsPrec :: Int -> ReadS Newline Source # readList :: ReadS [Newline] Source # readPrec :: ReadPrec Newline Source # readListPrec :: ReadPrec [Newline] Source #
Show Newline Source # | Since: base-4.3.0.0
Instance details Defined in GHC.IO.Handle.Types Methods showsPrec :: Int -> Newline -> ShowS Source # show :: Newline -> String Source # showList :: [Newline] -> ShowS Source #
Eq Newline Source # | Since: base-4.2.0.0
Instance details Defined in GHC.IO.Handle.Types Methods (==) :: Newline -> Newline -> Bool Source # (/=) :: Newline -> Newline -> Bool Source #
Ord Newline Source # | Since: base-4.3.0.0
Instance details Defined in GHC.IO.Handle.Types Methods compare :: Newline -> Newline -> Ordering Source # (<) :: Newline -> Newline -> Bool Source # (<=) :: Newline -> Newline -> Bool Source # (>) :: Newline -> Newline -> Bool Source # (>=) :: Newline -> Newline -> Bool Source # max :: Newline -> Newline -> Newline Source # min :: Newline -> Newline -> Newline Source #

nativeNewline :: Newline Source #

The native newline representation for the current platform: `LF` on Unix systems, `CRLF` on Windows.

universalNewlineMode :: NewlineMode Source #

Map `'\r\n'` into `'\n'` on input, and `'\n'` to the native newline representation on output. This mode can be used on any platform, and works with text files using any newline convention. The downside is that `readFile >>= writeFile` might yield a different file.

    universalNewlineMode  = NewlineMode { inputNL  = CRLF,
                                          outputNL = nativeNewline }

noNewlineTranslation :: NewlineMode Source #

Do no newline translation at all.

    noNewlineTranslation  = NewlineMode { inputNL  = LF, outputNL = LF }

nativeNewlineMode :: NewlineMode Source #

Use the native newline representation on both input and output

    nativeNewlineMode  = NewlineMode { inputNL  = nativeNewline
                                       outputNL = nativeNewline }