-- Unsafe IO operations
{-|
-This is the "back door" into the 'IO' monad, allowing
+This is the \"back door\" into the 'IO' monad, allowing
'IO' computation to be performed at any time. For
this to be safe, the 'IO' computation should be
free of side effects and independent of its environment.
effects take place (relative to the main I\/O trunk, or other calls to
'unsafePerformIO') is indeterminate. You have to be careful when
writing and compiling modules that use 'unsafePerformIO':
- * Use @{-# NOINLINE foo #-}@ as a pragma on any function @foo@
+
+ * Use @{\-\# NOINLINE foo \#-\}@ as a pragma on any function @foo@
that calls 'unsafePerformIO'. If the call is inlined,
- the I/O may be performed more than once.
+ the I\/O may be performed more than once.
* Use the compiler flag @-fno-cse@ to prevent common sub-expression
elimination being performed on the module, which might combine
'unsafeInterleaveIO' allows 'IO' computation to be deferred lazily.
When passed a value of type @IO a@, the 'IO' will only be performed
when the value of the @a@ is demanded. This is used to implement lazy
-file reading, see 'IO.hGetContents'.
+file reading, see 'System.IO.hGetContents'.
-}
{-# NOINLINE unsafeInterleaveIO #-}
unsafeInterleaveIO :: IO a -> IO a
-- 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
-- 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
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
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)
-- ---------------------------------------------------------------------------
-- IORefs
-- |A mutable variable in the 'IO' monad
-newtype IORef a = IORef (STRef RealWorld a) deriving Eq
+newtype IORef a = IORef (STRef RealWorld a)
+
+-- explicit instance because Haddock can't figure out a derived one
+instance Eq (IORef a) where
+ IORef x == IORef y = x == y
-- |Build a new 'IORef'
newIORef :: a -> IO (IORef a)
writeIORef (IORef var) v = stToIO (writeSTRef var v)
-- ---------------------------------------------------------------------------
+-- | An 'IOArray' is a mutable, boxed, non-strict array in the 'IO' monad.
+-- The type arguments are as follows:
+--
+-- * @i@: the index type of the array (should be an instance of 'Ix')
+--
+-- * @e@: the element type of the array.
+--
+--
+
+newtype IOArray i e = IOArray (STArray RealWorld i e)
+
+-- explicit instance because Haddock can't figure out a derived one
+instance Eq (IOArray i e) where
+ IOArray x == IOArray y = x == y
+
+-- |Build a new 'IOArray'
+newIOArray :: Ix i => (i,i) -> e -> IO (IOArray i e)
+{-# INLINE newIOArray #-}
+newIOArray lu init = stToIO $ do {marr <- newSTArray lu init; return (IOArray marr)}
+
+-- | Read a value from an 'IOArray'
+unsafeReadIOArray :: Ix i => IOArray i e -> Int -> IO e
+{-# INLINE unsafeReadIOArray #-}
+unsafeReadIOArray (IOArray marr) i = stToIO (unsafeReadSTArray marr i)
+
+-- | Write a new value into an 'IOArray'
+unsafeWriteIOArray :: Ix i => IOArray i e -> Int -> e -> IO ()
+{-# INLINE unsafeWriteIOArray #-}
+unsafeWriteIOArray (IOArray marr) i e = stToIO (unsafeWriteSTArray marr i e)
+
+-- | Read a value from an 'IOArray'
+readIOArray :: Ix i => IOArray i e -> i -> IO e
+readIOArray (IOArray marr) i = stToIO (readSTArray marr i)
+
+-- | Write a new value into an 'IOArray'
+writeIOArray :: Ix i => IOArray i e -> i -> e -> IO ()
+writeIOArray (IOArray marr) i e = stToIO (writeSTArray marr i e)
+
+
+-- ---------------------------------------------------------------------------
-- Show instance for Handles
-- handle types are 'show'n when printing error msgs, so
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
-- has a constructor in the 'Exception' type, and values of other
-- types may be injected into 'Exception' by coercing them to
-- 'Dynamic' (see the section on Dynamic Exceptions: "Control.Exception\#DynamicExceptions").
---
--- For backwards compatibility with Haskell 98, 'IOError' is a type synonym
--- for 'Exception'.
data Exception
= ArithException ArithException
-- ^Exceptions raised by arithmetic
-- operations. (NOTE: GHC currently does not throw
- -- 'ArithException's).
+ -- 'ArithException's except for 'DivideByZero').
| ArrayException ArrayException
-- ^Exceptions raised by array-related
-- operations. (NOTE: GHC currently does not throw
-- argument of 'ErrorCall' is the string passed to 'error' when it was
-- called.
| ExitException ExitCode
- -- ^The 'ExitException' exception is thrown by 'System.exitWith' (and
- -- 'System.exitFailure'). The 'ExitCode' argument is the value passed
- -- to 'System.exitWith'. An unhandled 'ExitException' exception in the
+ -- ^The 'ExitException' exception is thrown by 'System.Exit.exitWith' (and
+ -- 'System.Exit.exitFailure'). The 'ExitCode' argument is the value passed
+ -- to 'System.Exit.exitWith'. An unhandled 'ExitException' exception in the
-- main thread will cause the program to be terminated with the given
-- exit code.
| IOException IOException
BlockedOnDeadMVar == BlockedOnDeadMVar = True
NonTermination == NonTermination = True
Deadlock == Deadlock = True
+ _ == _ = False
-- -----------------------------------------------------------------------------
-- The ExitCode type
-- | A variant of 'throw' that can be used within the 'IO' monad.
--
--- Although 'ioError' has a type that is an instance of the type of 'throw', the
+-- Although 'throwIO' has a type that is an instance of the type of 'throw', the
-- two functions are subtly different:
--
-- > throw e `seq` return () ===> throw e
--- > ioError e `seq` return () ===> return ()
+-- > throwIO e `seq` return () ===> return ()
--
-- The first example will cause the exception @e@ to be raised,
--- whereas the second one won\'t. In fact, 'ioError' will only cause
+-- whereas the second one won\'t. In fact, 'throwIO' will only cause
-- an exception to be raised when it is used within the 'IO' monad.
--- The 'ioError' variant should be used in preference to 'throw' to
+-- The 'throwIO' variant should be used in preference to 'throw' to
-- raise an exception within the 'IO' monad because it guarantees
-- ordering with respect to other 'IO' operations, whereas 'throw'
-- does not.
-ioError :: Exception -> IO a
-ioError err = IO $ \s -> throw err s
+throwIO :: Exception -> IO a
+throwIO err = IO $ raiseIO# err
ioException :: IOException -> IO a
-ioException err = IO $ \s -> throw (IOException err) s
+ioException err = IO $ raiseIO# (IOException err)
+
+ioError :: IOError -> IO a
+ioError = ioException
-- ---------------------------------------------------------------------------
-- IOError type
--- A value @IOError@ encode errors occurred in the @IO@ monad.
--- An @IOError@ records a more specific error type, a descriptive
+-- | The Haskell 98 type for exceptions in the @IO@ monad.
+-- In Haskell 98, this is an opaque type.
+type IOError = IOException
+
+-- |Exceptions that occur in the @IO@ monad.
+-- An @IOException@ records a more specific error type, a descriptive
-- string and maybe the handle that was used when the error was
-- flagged.
-
-type IOError = Exception
-
data IOException
= IOError {
ioe_handle :: Maybe Handle, -- the handle used by the action flagging
-- the error.
ioe_type :: IOErrorType, -- what it was.
ioe_location :: String, -- location.
- ioe_descr :: String, -- error type specific information.
+ ioe_description :: String, -- error type specific information.
ioe_filename :: Maybe FilePath -- filename the error is related to.
}
x == y =
case x of
DynIOError{} -> False -- from a strictness POV, compatible with a derived Eq inst?
- _ -> getTag# x ==# getTag# y
+ _ -> getTag x ==# getTag y
instance Show IOErrorType where
showsPrec _ e =
DynIOError{} -> "unknown IO error"
userError :: String -> IOError
-userError str = IOException (IOError Nothing UserError "" str Nothing)
+userError str = IOError Nothing UserError "" str Nothing
-- ---------------------------------------------------------------------------
-- Showing IOErrors
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
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