X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=GHC%2FIOBase.lhs;h=187014621e7d65a7c6fbdc159e11aec359cb28a4;hb=b72dda8318394f238214364dc01b8963599f8cd6;hp=43073c02861fd56ec0569b80e95dd7e5b46fff5b;hpb=ae826792516f76f4a35d74c885653167f2045df9;p=haskell-directory.git diff --git a/GHC/IOBase.lhs b/GHC/IOBase.lhs index 43073c0..1870146 100644 --- a/GHC/IOBase.lhs +++ b/GHC/IOBase.lhs @@ -220,11 +220,42 @@ instance Eq (MVar a) where -- Note: when a Handle is garbage collected, we want to flush its buffer -- and close the OS file handle, so as to free up a (precious) resource. +-- | 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. + data Handle = FileHandle -- A normal handle to a file + FilePath -- the file (invariant) !(MVar Handle__) | DuplexHandle -- A handle to a read/write stream + FilePath -- file for a FIFO, otherwise some + -- descriptive string. !(MVar Handle__) -- The read side !(MVar Handle__) -- The write side @@ -233,8 +264,8 @@ data Handle -- seekable. instance Eq Handle where - (FileHandle h1) == (FileHandle h2) = h1 == h2 - (DuplexHandle h1 _) == (DuplexHandle h2 _) = h1 == h2 + (FileHandle _ h1) == (FileHandle _ h2) = h1 == h2 + (DuplexHandle _ h1 _) == (DuplexHandle _ h2 _) = h1 == h2 _ == _ = False type FD = Int -- XXX ToDo: should be CInt @@ -246,7 +277,6 @@ data Handle__ haIsBin :: Bool, -- binary mode? haIsStream :: Bool, -- is this a stream handle? haBufferMode :: BufferMode, -- buffer contains read/write data? - haFilePath :: FilePath, -- file name, possibly haBuffer :: !(IORef Buffer), -- the current buffer haBuffers :: !(IORef BufferList), -- spare buffers haOtherSide :: Maybe (MVar Handle__) -- ptr to the write side of a @@ -338,53 +368,63 @@ isWritableHandleType WriteHandle = True isWritableHandleType ReadWriteHandle = True isWritableHandleType _ = False --- File names are specified using @FilePath@, a OS-dependent --- string that (hopefully, I guess) maps to an accessible file/object. +-- | File and directory names are values of type 'String', whose precise +-- meaning is operating system dependent. Files can be opened, yielding a +-- handle which can then be used to operate on the contents of that file. type FilePath = String -- --------------------------------------------------------------------------- -- Buffering modes --- Three kinds of buffering are supported: line-buffering, +-- | 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 from the internal --- buffer according to the buffer mode: +-- effects. For output, items are written out, or /flushed/, +-- from the internal buffer according to the buffer mode: -- --- o line-buffering the entire output buffer is written --- out whenever a newline is output, the output buffer overflows, --- a flush is issued, or the handle is closed. +-- * /line-buffering/: the entire output buffer is flushed +-- whenever a newline is output, the buffer overflows, +-- a 'System.IO.hFlush' is issued, or the handle is closed. -- --- o block-buffering the entire output buffer is written out whenever --- it overflows, a flush is issued, or the handle --- is closed. +-- * /block-buffering/: the entire buffer is written out whenever it +-- overflows, a 'System.IO.hFlush' is issued, or the handle is closed. -- --- o no-buffering output is written immediately, and never stored --- in the output buffer. +-- * /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 handle {\em hdl}. - --- o line-buffering when the input buffer for the handle is not empty, --- the next item is obtained from the buffer; --- otherwise, when the input 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. -- --- o block-buffering when the input buffer for the handle becomes empty, --- the next block of data is read into this buffer. +-- * /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. -- --- o no-buffering the next input item is read and returned. - +-- * /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. (the IO interface provides --- operations for changing the default buffering of a handle tho.) +-- and terminals will normally be line-buffered. data BufferMode - = NoBuffering | LineBuffering | BlockBuffering (Maybe Int) + = 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. deriving (Eq, Ord, Read, Show) -- --------------------------------------------------------------------------- @@ -467,46 +507,10 @@ instance Show HandleType where ReadWriteHandle -> showString "read-writable" instance Show Handle where - showsPrec p (FileHandle h) = showHandle p h False - showsPrec p (DuplexHandle _ h) = showHandle p h True - -showHandle p h duplex = - let - -- (Big) SIGH: unfolded defn of takeMVar to avoid - -- an (oh-so) unfortunate module loop with GHC.Conc. - hdl_ = unsafePerformIO (IO $ \ s# -> - case h of { MVar h# -> - case takeMVar# h# s# of { (# s2# , r #) -> - case putMVar# h# r s2# of { s3# -> - (# s3#, r #) }}}) - - showType | duplex = showString "duplex (read-write)" - | otherwise = showsPrec p (haType hdl_) - in - showChar '{' . - showHdl (haType hdl_) - (showString "loc=" . showString (haFilePath hdl_) . showChar ',' . - showString "type=" . showType . showChar ',' . - showString "binary=" . showsPrec p (haIsBin hdl_) . showChar ',' . - showString "buffering=" . showBufMode (unsafePerformIO (readIORef (haBuffer hdl_))) (haBufferMode hdl_) . showString "}" ) - where - - showHdl :: HandleType -> ShowS -> ShowS - showHdl ht cont = - case ht of - ClosedHandle -> showsPrec p ht . showString "}" - _ -> cont - - showBufMode :: Buffer -> BufferMode -> ShowS - showBufMode buf bmo = - case bmo of - NoBuffering -> showString "none" - LineBuffering -> showString "line" - BlockBuffering (Just n) -> showString "block " . showParen True (showsPrec p n) - BlockBuffering Nothing -> showString "block " . showParen True (showsPrec p def) - where - def :: Int - def = bufSize buf + showsPrec p (FileHandle file _) = showHandle file + showsPrec p (DuplexHandle file _ _) = showHandle file + +showHandle file = showString "{handle: " . showString file . showString "}" -- ------------------------------------------------------------------------ -- Exception datatype and operations @@ -830,19 +834,18 @@ userError str = IOError Nothing UserError "" str Nothing instance Show IOException where showsPrec p (IOError hdl iot loc s fn) = - showsPrec p iot . + (case fn of + Nothing -> case hdl of + Nothing -> id + Just h -> showsPrec p h . showString ": " + Just name -> showString name . showString ": ") . (case loc of "" -> id - _ -> showString "\nAction: " . showString loc) . - (case hdl of - Nothing -> id - Just h -> showString "\nHandle: " . showsPrec p h) . + _ -> showString loc . showString ": ") . + showsPrec p iot . (case s of "" -> id - _ -> showString "\nReason: " . showString s) . - (case fn of - Nothing -> id - Just name -> showString "\nFile: " . showString name) + _ -> showString " (" . showString s . showString ")") -- ----------------------------------------------------------------------------- -- IOMode type