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 |
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.(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
- isReadableHandleType :: HandleType -> Bool
- isWritableHandleType :: HandleType -> Bool
- isReadWriteHandleType :: HandleType -> Bool
- data BufferMode
- data BufferCodec from to state = BufferCodec {}
- data NewlineMode = NewlineMode {}
- data Newline
- nativeNewline :: Newline
- universalNewlineMode :: NewlineMode
- noNewlineTranslation :: NewlineMode
- nativeNewlineMode :: NewlineMode
Documentation
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.
forall dev enc_state dec_state.(IODevice dev, BufferedIO dev, Typeable dev) => Handle__ | |
|
checkHandleInvariants :: Handle__ -> IO () Source #
data BufferList e Source #
data HandleType Source #
Instances
Show HandleType Source # | Since: 4.1.0.0 |
Defined in GHC.IO.Handle.Types |
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.
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 |
Instances
Eq BufferMode Source # | Since: 4.2.0.0 |
Defined in GHC.IO.Handle.Types (==) :: BufferMode -> BufferMode -> Bool # (/=) :: BufferMode -> BufferMode -> Bool # | |
Ord BufferMode Source # | Since: 4.2.0.0 |
Defined in GHC.IO.Handle.Types compare :: BufferMode -> BufferMode -> Ordering # (<) :: BufferMode -> BufferMode -> Bool # (<=) :: BufferMode -> BufferMode -> Bool # (>) :: BufferMode -> BufferMode -> Bool # (>=) :: BufferMode -> BufferMode -> Bool # max :: BufferMode -> BufferMode -> BufferMode # min :: BufferMode -> BufferMode -> BufferMode # | |
Read BufferMode Source # | Since: 4.2.0.0 |
Defined in GHC.IO.Handle.Types | |
Show BufferMode Source # | Since: 4.2.0.0 |
Defined in GHC.IO.Handle.Types |
data BufferCodec from to state Source #
BufferCodec | |
|
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.
Instances
Eq NewlineMode Source # | Since: 4.2.0.0 |
Defined in GHC.IO.Handle.Types (==) :: NewlineMode -> NewlineMode -> Bool # (/=) :: NewlineMode -> NewlineMode -> Bool # | |
Ord NewlineMode Source # | Since: 4.3.0.0 |
Defined in GHC.IO.Handle.Types compare :: NewlineMode -> NewlineMode -> Ordering # (<) :: NewlineMode -> NewlineMode -> Bool # (<=) :: NewlineMode -> NewlineMode -> Bool # (>) :: NewlineMode -> NewlineMode -> Bool # (>=) :: NewlineMode -> NewlineMode -> Bool # max :: NewlineMode -> NewlineMode -> NewlineMode # min :: NewlineMode -> NewlineMode -> NewlineMode # | |
Read NewlineMode Source # | Since: 4.3.0.0 |
Defined in GHC.IO.Handle.Types | |
Show NewlineMode Source # | Since: 4.3.0.0 |
Defined in GHC.IO.Handle.Types |
The representation of a newline in the external file or stream.
universalNewlineMode :: NewlineMode Source #
Map '\r\n'
into '\n'
on input, and '\n'
to the native newline
represetnation 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 }