directory-1.3.6.1: Platform-agnostic library for filesystem operations
Stabilityunstable
Portabilityportable
Safe HaskellSafe-Inferred
LanguageHaskell2010

System.Directory.Internal.Prelude

Description

Internal modules are always subject to change from version to version.

Synopsis

Documentation

module Prelude

second :: Arrow a => a b c -> a (d, b) (d, c) Source #

A mirror image of first.

The default definition may be overridden with a more efficient version if desired.

killThread :: ThreadId -> IO () Source #

killThread raises the ThreadKilled exception in the given thread (GHC only).

killThread tid = throwTo tid ThreadKilled

forkIO :: IO () -> IO ThreadId Source #

Creates a new thread to run the IO computation passed as the first argument, and returns the ThreadId of the newly created thread.

The new thread will be a lightweight, unbound thread. Foreign calls made by this thread are not guaranteed to be made by any particular OS thread; if you need foreign calls to be made by a particular OS thread, then use forkOS instead.

The new thread inherits the masked state of the parent (see mask).

The newly created thread has an exception handler that discards the exceptions BlockedIndefinitelyOnMVar, BlockedIndefinitelyOnSTM, and ThreadKilled, and passes all other exceptions to the uncaught exception handler.

putMVar :: MVar a -> a -> IO () Source #

Put a value into an MVar. If the MVar is currently full, putMVar will wait until it becomes empty.

There are two further important properties of putMVar:

  • putMVar is single-wakeup. That is, if there are multiple threads blocked in putMVar, and the MVar becomes empty, only one thread will be woken up. The runtime guarantees that the woken thread completes its putMVar operation.
  • When multiple threads are blocked on an MVar, they are woken up in FIFO order. This is useful for providing fairness properties of abstractions built using MVars.

readMVar :: MVar a -> IO a Source #

Atomically read the contents of an MVar. If the MVar is currently empty, readMVar will wait until it is full. readMVar is guaranteed to receive the next putMVar.

readMVar is multiple-wakeup, so when multiple readers are blocked on an MVar, all of them are woken up at the same time.

Compatibility note: Prior to base 4.7, readMVar was a combination of takeMVar and putMVar. This mean that in the presence of other threads attempting to putMVar, readMVar could block. Furthermore, readMVar would not receive the next putMVar if there was already a pending thread blocked on takeMVar. The old behavior can be recovered by implementing 'readMVar as follows:

 readMVar :: MVar a -> IO a
 readMVar m =
   mask_ $ do
     a <- takeMVar m
     putMVar m a
     return a

takeMVar :: MVar a -> IO a Source #

Return the contents of the MVar. If the MVar is currently empty, takeMVar will wait until it is full. After a takeMVar, the MVar is left empty.

There are two further important properties of takeMVar:

  • takeMVar is single-wakeup. That is, if there are multiple threads blocked in takeMVar, and the MVar becomes full, only one thread will be woken up. The runtime guarantees that the woken thread completes its takeMVar operation.
  • When multiple threads are blocked on an MVar, they are woken up in FIFO order. This is useful for providing fairness properties of abstractions built using MVars.

newEmptyMVar :: IO (MVar a) Source #

Create an MVar which is initially empty.

bracket_ :: IO a -> IO b -> IO c -> IO c Source #

A variant of bracket where the return value from the first computation is not required.

finally Source #

Arguments

:: IO a

computation to run first

-> IO b

computation to run afterward (even if an exception was raised)

-> IO a 

A specialised variant of bracket with just a computation to run afterward.

bracket Source #

Arguments

:: IO a

computation to run first ("acquire resource")

-> (a -> IO b)

computation to run last ("release resource")

-> (a -> IO c)

computation to run in-between

-> IO c 

When you want to acquire a resource, do some work with it, and then release the resource, it is a good idea to use bracket, because bracket will install the necessary exception handler to release the resource in the event that an exception is raised during the computation. If an exception is raised, then bracket will re-raise the exception (after performing the release).

A common example is opening a file:

bracket
  (openFile "filename" ReadMode)
  (hClose)
  (\fileHandle -> do { ... })

The arguments to bracket are in this order so that we can partially apply it, e.g.:

withFile name mode = bracket (openFile name mode) hClose

onException :: IO a -> IO b -> IO a Source #

Like finally, but only performs the final action if there was an exception raised by the computation.

try :: Exception e => IO a -> IO (Either e a) Source #

Similar to catch, but returns an Either result which is (Right a) if no exception of type e was raised, or (Left ex) if an exception of type e was raised and its value is ex. If any other type of exception is raised then it will be propagated up to the next enclosing exception handler.

 try a = catch (Right `liftM` a) (return . Left)

mask :: ((forall a. IO a -> IO a) -> IO b) -> IO b Source #

Executes an IO computation with asynchronous exceptions masked. That is, any thread which attempts to raise an exception in the current thread with throwTo will be blocked until asynchronous exceptions are unmasked again.

The argument passed to mask is a function that takes as its argument another function, which can be used to restore the prevailing masking state within the context of the masked computation. For example, a common way to use mask is to protect the acquisition of a resource:

mask $ \restore -> do
    x <- acquire
    restore (do_something_with x) `onException` release
    release

This code guarantees that acquire is paired with release, by masking asynchronous exceptions for the critical parts. (Rather than write this code yourself, it would be better to use bracket which abstracts the general pattern).

Note that the restore action passed to the argument to mask does not necessarily unmask asynchronous exceptions, it just restores the masking state to that of the enclosing context. Thus if asynchronous exceptions are already masked, mask cannot be used to unmask exceptions again. This is so that if you call a library function with exceptions masked, you can be sure that the library call will not be able to unmask exceptions again. If you are writing library code and need to use asynchronous exceptions, the only way is to create a new thread; see forkIOWithUnmask.

Asynchronous exceptions may still be received while in the masked state if the masked thread blocks in certain ways; see Control.Exception.

Threads created by forkIO inherit the MaskingState from the parent; that is, to start a thread in the MaskedInterruptible state, use mask_ $ forkIO .... This is particularly useful if you need to establish an exception handler in the forked thread before any asynchronous exceptions are received. To create a new thread in an unmasked state use forkIOWithUnmask.

throwIO :: Exception e => e -> IO a Source #

A variant of throw that can only be used within the IO monad.

Although throwIO has a type that is an instance of the type of throw, the two functions are subtly different:

throw e   `seq` x  ===> throw e
throwIO e `seq` x  ===> x

The first example will cause the exception e to be raised, 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 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.

catch Source #

Arguments

:: Exception e 
=> IO a

The computation to run

-> (e -> IO a)

Handler to invoke if an exception is raised

-> IO a 

This is the simplest of the exception-catching functions. It takes a single argument, runs it, and if an exception is raised the "handler" is executed, with the value of the exception passed as an argument. Otherwise, the result is returned as normal. For example:

  catch (readFile f)
        (\e -> do let err = show (e :: IOException)
                  hPutStr stderr ("Warning: Couldn't open " ++ f ++ ": " ++ err)
                  return "")

Note that we have to give a type signature to e, or the program will not typecheck as the type is ambiguous. While it is possible to catch exceptions of any type, see the section "Catching all exceptions" (in Control.Exception) for an explanation of the problems with doing so.

For catching exceptions in pure (non-IO) expressions, see the function evaluate.

Note that due to Haskell's unspecified evaluation order, an expression may throw one of several possible exceptions: consider the expression (error "urk") + (1 `div` 0). Does the expression throw ErrorCall "urk", or DivideByZero?

The answer is "it might throw either"; the choice is non-deterministic. If you are catching any type of exception then you might catch either. If you are calling catch with type IO Int -> (ArithException -> IO Int) -> IO Int then the handler may get run with DivideByZero as an argument, or an ErrorCall "urk" exception may be propagated further up. If you call it again, you might get the opposite behaviour. This is ok, because catch is an IO computation.

data SomeException Source #

The SomeException type is the root of the exception type hierarchy. When an exception of type e is thrown, behind the scenes it is encapsulated in a SomeException.

unless :: Applicative f => Bool -> f () -> f () Source #

The reverse of when.

replicateM_ :: Applicative m => Int -> m a -> m () Source #

Like replicateM, but discards the result.

(<=<) :: Monad m => (b -> m c) -> (a -> m b) -> a -> m c infixr 1 Source #

Right-to-left composition of Kleisli arrows. (>=>), with the arguments flipped.

Note how this operator resembles function composition (.):

(.)   ::            (b ->   c) -> (a ->   b) -> a ->   c
(<=<) :: Monad m => (b -> m c) -> (a -> m b) -> a -> m c

(>=>) :: Monad m => (a -> m b) -> (b -> m c) -> a -> m c infixr 1 Source #

Left-to-right composition of Kleisli arrows.

'(bs >=> cs) a' can be understood as the do expression

do b <- bs a
   cs b

when :: Applicative f => Bool -> f () -> f () Source #

Conditional execution of Applicative expressions. For example,

when debug (putStrLn "Debugging")

will output the string Debugging if the Boolean value debug is True, and otherwise do nothing.

complement :: Bits a => a -> a Source #

Reverse all the bits in the argument

(.&.) :: Bits a => a -> a -> a infixl 7 Source #

Bitwise "and"

(.|.) :: Bits a => a -> a -> a infixl 5 Source #

Bitwise "or"

toUpper :: Char -> Char Source #

Convert a letter to the corresponding upper-case letter, if any. Any other character is returned unchanged.

toLower :: Char -> Char Source #

Convert a letter to the corresponding lower-case letter, if any. Any other character is returned unchanged.

isAlpha :: Char -> Bool Source #

Selects alphabetic Unicode characters (lower-case, upper-case and title-case letters, plus letters of caseless scripts and modifiers letters). This function is equivalent to isLetter.

isAscii :: Char -> Bool Source #

Selects the first 128 characters of the Unicode character set, corresponding to the ASCII character set.

for_ :: (Foldable t, Applicative f) => t a -> (a -> f b) -> f () Source #

for_ is traverse_ with its arguments flipped. For a version that doesn't ignore the results see for.

Examples

Expand

Basic usage:

>>> for_ [1..4] print
1
2
3
4

traverse_ :: (Foldable t, Applicative f) => (a -> f b) -> t a -> f () Source #

Map each element of a structure to an action, evaluate these actions from left to right, and ignore the results. For a version that doesn't ignore the results see traverse.

Examples

Expand

Basic usage:

>>> traverse_ print ["Hello", "world", "!"]
"Hello"
"world"
"!"

on :: (b -> b -> c) -> (a -> b) -> a -> a -> c infixl 0 Source #

on b u x y runs the binary function b on the results of applying unary function u to two arguments x and y. From the opposite perspective, it transforms two inputs and combines the outputs.

((+) `on` f) x y = f x + f y

Typical usage: sortBy (compare `on` fst).

Algebraic properties:

  • (*) `on` id = (*) -- (if (*) ∉ {⊥, const ⊥})
  • ((*) `on` f) `on` g = (*) `on` (f . g)
  • flip on f . flip on g = flip on (g . f)

catMaybes :: [Maybe a] -> [a] Source #

The catMaybes function takes a list of Maybes and returns a list of all the Just values.

Examples

Expand

Basic usage:

>>> catMaybes [Just 1, Nothing, Just 3]
[1,3]

When constructing a list of Maybe values, catMaybes can be used to return all of the "success" results (if the list is the result of a map, then mapMaybe would be more appropriate):

>>> import Text.Read ( readMaybe )
>>> [readMaybe x :: Maybe Int | x <- ["1", "Foo", "3"] ]
[Just 1,Nothing,Just 3]
>>> catMaybes $ [readMaybe x :: Maybe Int | x <- ["1", "Foo", "3"] ]
[1,3]

maybeToList :: Maybe a -> [a] Source #

The maybeToList function returns an empty list when given Nothing or a singleton list when given Just.

Examples

Expand

Basic usage:

>>> maybeToList (Just 7)
[7]
>>> maybeToList Nothing
[]

One can use maybeToList to avoid pattern matching when combined with a function that (safely) works on lists:

>>> import Text.Read ( readMaybe )
>>> sum $ maybeToList (readMaybe "3")
3
>>> sum $ maybeToList (readMaybe "")
0

fromMaybe :: a -> Maybe a -> a Source #

The fromMaybe function takes a default value and a Maybe value. If the Maybe is Nothing, it returns the default value; otherwise, it returns the value contained in the Maybe.

Examples

Expand

Basic usage:

>>> fromMaybe "" (Just "Hello, World!")
"Hello, World!"
>>> fromMaybe "" Nothing
""

Read an integer from a string using readMaybe. If we fail to parse an integer, we want to return 0 by default:

>>> import Text.Read ( readMaybe )
>>> fromMaybe 0 (readMaybe "5")
5
>>> fromMaybe 0 (readMaybe "")
0

(<>) :: Semigroup a => a -> a -> a infixr 6 Source #

An associative operation.

>>> [1,2,3] <> [4,5,6]
[1,2,3,4,5,6]

mempty :: Monoid a => a Source #

Identity of mappend

>>> "Hello world" <> mempty
"Hello world"

mconcat :: Monoid a => [a] -> a Source #

Fold a list using the monoid.

For most types, the default definition for mconcat will be used, but the function is included in the class definition so that an optimized version can be provided for specific types.

>>> mconcat ["Hello", " ", "Haskell", "!"]
"Hello Haskell!"

writeIORef :: IORef a -> a -> IO () Source #

Write a new value into an IORef

readIORef :: IORef a -> IO a Source #

Read the value of an IORef

newIORef :: a -> IO (IORef a) Source #

Build a new IORef

data IORef a Source #

A mutable variable in the IO monad

Instances

Instances details
Eq (IORef a)

Pointer equality.

Since: base-4.0.0.0

Instance details

Defined in GHC.IORef

Methods

(==) :: IORef a -> IORef a -> Bool #

(/=) :: IORef a -> IORef a -> Bool #

for :: (Traversable t, Applicative f) => t a -> (a -> f b) -> f (t b) Source #

for is traverse with its arguments flipped. For a version that ignores the results see for_.

data Ptr a Source #

A value of type Ptr a represents a pointer to an object, or an array of objects, which may be marshalled to or from Haskell values of type a.

The type a will often be an instance of class Storable which provides the marshalling operations. However this is not essential, and you can provide your own operations to access the pointer. For example you might write small foreign functions to get or set the fields of a C struct.

Instances

Instances details
Eq (Ptr a)

Since: base-2.1

Instance details

Defined in GHC.Ptr

Methods

(==) :: Ptr a -> Ptr a -> Bool #

(/=) :: Ptr a -> Ptr a -> Bool #

Ord (Ptr a)

Since: base-2.1

Instance details

Defined in GHC.Ptr

Methods

compare :: Ptr a -> Ptr a -> Ordering #

(<) :: Ptr a -> Ptr a -> Bool #

(<=) :: Ptr a -> Ptr a -> Bool #

(>) :: Ptr a -> Ptr a -> Bool #

(>=) :: Ptr a -> Ptr a -> Bool #

max :: Ptr a -> Ptr a -> Ptr a #

min :: Ptr a -> Ptr a -> Ptr a #

Show (Ptr a)

Since: base-2.1

Instance details

Defined in GHC.Ptr

Methods

showsPrec :: Int -> Ptr a -> ShowS Source #

show :: Ptr a -> String Source #

showList :: [Ptr a] -> ShowS Source #

Foldable (UAddr :: Type -> Type)

Since: base-4.9.0.0

Instance details

Defined in Data.Foldable

Methods

fold :: Monoid m => UAddr m -> m Source #

foldMap :: Monoid m => (a -> m) -> UAddr a -> m Source #

foldMap' :: Monoid m => (a -> m) -> UAddr a -> m Source #

foldr :: (a -> b -> b) -> b -> UAddr a -> b Source #

foldr' :: (a -> b -> b) -> b -> UAddr a -> b Source #

foldl :: (b -> a -> b) -> b -> UAddr a -> b Source #

foldl' :: (b -> a -> b) -> b -> UAddr a -> b Source #

foldr1 :: (a -> a -> a) -> UAddr a -> a Source #

foldl1 :: (a -> a -> a) -> UAddr a -> a Source #

toList :: UAddr a -> [a] Source #

null :: UAddr a -> Bool Source #

length :: UAddr a -> Int Source #

elem :: Eq a => a -> UAddr a -> Bool Source #

maximum :: Ord a => UAddr a -> a Source #

minimum :: Ord a => UAddr a -> a Source #

sum :: Num a => UAddr a -> a Source #

product :: Num a => UAddr a -> a Source #

Traversable (UAddr :: Type -> Type)

Since: base-4.9.0.0

Instance details

Defined in Data.Traversable

Methods

traverse :: Applicative f => (a -> f b) -> UAddr a -> f (UAddr b) Source #

sequenceA :: Applicative f => UAddr (f a) -> f (UAddr a) Source #

mapM :: Monad m => (a -> m b) -> UAddr a -> m (UAddr b) Source #

sequence :: Monad m => UAddr (m a) -> m (UAddr a) Source #

Storable (Ptr a)

Since: base-2.1

Instance details

Defined in Foreign.Storable

Methods

sizeOf :: Ptr a -> Int Source #

alignment :: Ptr a -> Int Source #

peekElemOff :: Ptr (Ptr a) -> Int -> IO (Ptr a) Source #

pokeElemOff :: Ptr (Ptr a) -> Int -> Ptr a -> IO () Source #

peekByteOff :: Ptr b -> Int -> IO (Ptr a) Source #

pokeByteOff :: Ptr b -> Int -> Ptr a -> IO () Source #

peek :: Ptr (Ptr a) -> IO (Ptr a) Source #

poke :: Ptr (Ptr a) -> Ptr a -> IO () Source #

withArray :: Storable a => [a] -> (Ptr a -> IO b) -> IO b Source #

Temporarily store a list of storable values in memory (like with, but for multiple elements).

allocaArray :: Storable a => Int -> (Ptr a -> IO b) -> IO b Source #

Temporarily allocate space for the given number of elements (like alloca, but for multiple elements).

maybeWith :: (a -> (Ptr b -> IO c) -> IO c) -> Maybe a -> (Ptr b -> IO c) -> IO c Source #

Converts a withXXX combinator into one marshalling a value wrapped into a Maybe, using nullPtr to represent Nothing.

with :: Storable a => a -> (Ptr a -> IO b) -> IO b Source #

with val f executes the computation f, passing as argument a pointer to a temporarily allocated block of memory into which val has been marshalled (the combination of alloca and poke).

The memory is freed when f terminates (either normally or via an exception), so the pointer passed to f must not be used after this.

allocaBytesAligned :: Int -> Int -> (Ptr a -> IO b) -> IO b Source #

allocaBytes :: Int -> (Ptr a -> IO b) -> IO b Source #

allocaBytes n f executes the computation f, passing as argument a pointer to a temporarily allocated block of memory of n bytes. The block of memory is sufficiently aligned for any of the basic foreign types that fits into a memory block of the allocated size.

The memory is freed when f terminates (either normally or via an exception), so the pointer passed to f must not be used after this.

alloca :: Storable a => (Ptr a -> IO b) -> IO b Source #

alloca f executes the computation f, passing as argument a pointer to a temporarily allocated block of memory sufficient to hold values of type a.

The memory is freed when f terminates (either normally or via an exception), so the pointer passed to f must not be used after this.

class Storable a where Source #

The member functions of this class facilitate writing values of primitive types to raw memory (which may have been allocated with the above mentioned routines) and reading values from blocks of raw memory. The class, furthermore, includes support for computing the storage requirements and alignment restrictions of storable types.

Memory addresses are represented as values of type Ptr a, for some a which is an instance of class Storable. The type argument to Ptr helps provide some valuable type safety in FFI code (you can't mix pointers of different types without an explicit cast), while helping the Haskell type system figure out which marshalling method is needed for a given pointer.

All marshalling between Haskell and a foreign language ultimately boils down to translating Haskell data structures into the binary representation of a corresponding data structure of the foreign language and vice versa. To code this marshalling in Haskell, it is necessary to manipulate primitive data types stored in unstructured memory blocks. The class Storable facilitates this manipulation on all types for which it is instantiated, which are the standard basic types of Haskell, the fixed size Int types (Int8, Int16, Int32, Int64), the fixed size Word types (Word8, Word16, Word32, Word64), StablePtr, all types from Foreign.C.Types, as well as Ptr.

Minimal complete definition

sizeOf, alignment, (peek | peekElemOff | peekByteOff), (poke | pokeElemOff | pokeByteOff)

Methods

sizeOf :: a -> Int Source #

Computes the storage requirements (in bytes) of the argument. The value of the argument is not used.

alignment :: a -> Int Source #

Computes the alignment constraint of the argument. An alignment constraint x is fulfilled by any address divisible by x. The value of the argument is not used.

peekElemOff :: Ptr a -> Int -> IO a Source #

Read a value from a memory area regarded as an array of values of the same kind. The first argument specifies the start address of the array and the second the index into the array (the first element of the array has index 0). The following equality holds,

peekElemOff addr idx = IOExts.fixIO $ \result ->
  peek (addr `plusPtr` (idx * sizeOf result))

Note that this is only a specification, not necessarily the concrete implementation of the function.

pokeElemOff :: Ptr a -> Int -> a -> IO () Source #

Write a value to a memory area regarded as an array of values of the same kind. The following equality holds:

pokeElemOff addr idx x = 
  poke (addr `plusPtr` (idx * sizeOf x)) x

peekByteOff :: Ptr b -> Int -> IO a Source #

Read a value from a memory location given by a base address and offset. The following equality holds:

peekByteOff addr off = peek (addr `plusPtr` off)

pokeByteOff :: Ptr b -> Int -> a -> IO () Source #

Write a value to a memory location given by a base address and offset. The following equality holds:

pokeByteOff addr off x = poke (addr `plusPtr` off) x

peek :: Ptr a -> IO a Source #

Read a value from the given memory location.

Note that the peek and poke functions might require properly aligned addresses to function correctly. This is architecture dependent; thus, portable code should ensure that when peeking or poking values of some type a, the alignment constraint for a, as given by the function alignment is fulfilled.

poke :: Ptr a -> a -> IO () Source #

Write the given value to the given memory location. Alignment restrictions might apply; see peek.

Instances

Instances details
Storable Bool

Since: base-2.1

Instance details

Defined in Foreign.Storable

Storable Char

Since: base-2.1

Instance details

Defined in Foreign.Storable

Storable Double

Since: base-2.1

Instance details

Defined in Foreign.Storable

Storable Float

Since: base-2.1

Instance details

Defined in Foreign.Storable

Storable Int

Since: base-2.1

Instance details

Defined in Foreign.Storable

Storable Int8

Since: base-2.1

Instance details

Defined in Foreign.Storable

Storable Int16

Since: base-2.1

Instance details

Defined in Foreign.Storable

Storable Int32

Since: base-2.1

Instance details

Defined in Foreign.Storable

Storable Int64

Since: base-2.1

Instance details

Defined in Foreign.Storable

Storable Word

Since: base-2.1

Instance details

Defined in Foreign.Storable

Storable Word8

Since: base-2.1

Instance details

Defined in Foreign.Storable

Storable Word16

Since: base-2.1

Instance details

Defined in Foreign.Storable

Storable Word32

Since: base-2.1

Instance details

Defined in Foreign.Storable

Storable Word64

Since: base-2.1

Instance details

Defined in Foreign.Storable

Storable ()

Since: base-4.9.0.0

Instance details

Defined in Foreign.Storable

Methods

sizeOf :: () -> Int Source #

alignment :: () -> Int Source #

peekElemOff :: Ptr () -> Int -> IO () Source #

pokeElemOff :: Ptr () -> Int -> () -> IO () Source #

peekByteOff :: Ptr b -> Int -> IO () Source #

pokeByteOff :: Ptr b -> Int -> () -> IO () Source #

peek :: Ptr () -> IO () Source #

poke :: Ptr () -> () -> IO () Source #

Storable CDev 
Instance details

Defined in System.Posix.Types

Storable CIno 
Instance details

Defined in System.Posix.Types

Storable CMode 
Instance details

Defined in System.Posix.Types

Storable COff 
Instance details

Defined in System.Posix.Types

Storable CPid 
Instance details

Defined in System.Posix.Types

Storable CSsize 
Instance details

Defined in System.Posix.Types

Storable CGid 
Instance details

Defined in System.Posix.Types

Storable CNlink 
Instance details

Defined in System.Posix.Types

Storable CUid 
Instance details

Defined in System.Posix.Types

Storable CCc 
Instance details

Defined in System.Posix.Types

Storable CSpeed 
Instance details

Defined in System.Posix.Types

Storable CTcflag 
Instance details

Defined in System.Posix.Types

Storable CRLim 
Instance details

Defined in System.Posix.Types

Storable CBlkSize 
Instance details

Defined in System.Posix.Types

Storable CBlkCnt 
Instance details

Defined in System.Posix.Types

Storable CClockId 
Instance details

Defined in System.Posix.Types

Storable CFsBlkCnt 
Instance details

Defined in System.Posix.Types

Storable CFsFilCnt 
Instance details

Defined in System.Posix.Types

Storable CId 
Instance details

Defined in System.Posix.Types

Storable CKey 
Instance details

Defined in System.Posix.Types

Storable CTimer 
Instance details

Defined in System.Posix.Types

Storable CSocklen 
Instance details

Defined in System.Posix.Types

Storable CNfds 
Instance details

Defined in System.Posix.Types

Storable Fd 
Instance details

Defined in System.Posix.Types

Methods

sizeOf :: Fd -> Int Source #

alignment :: Fd -> Int Source #

peekElemOff :: Ptr Fd -> Int -> IO Fd Source #

pokeElemOff :: Ptr Fd -> Int -> Fd -> IO () Source #

peekByteOff :: Ptr b -> Int -> IO Fd Source #

pokeByteOff :: Ptr b -> Int -> Fd -> IO () Source #

peek :: Ptr Fd -> IO Fd Source #

poke :: Ptr Fd -> Fd -> IO () Source #

Storable CChar 
Instance details

Defined in Foreign.C.Types

Storable CSChar 
Instance details

Defined in Foreign.C.Types

Storable CUChar 
Instance details

Defined in Foreign.C.Types

Storable CShort 
Instance details

Defined in Foreign.C.Types

Storable CUShort 
Instance details

Defined in Foreign.C.Types

Storable CInt 
Instance details

Defined in Foreign.C.Types

Storable CUInt 
Instance details

Defined in Foreign.C.Types

Storable CLong 
Instance details

Defined in Foreign.C.Types

Storable CULong 
Instance details

Defined in Foreign.C.Types

Storable CLLong 
Instance details

Defined in Foreign.C.Types

Storable CULLong 
Instance details

Defined in Foreign.C.Types

Storable CBool 
Instance details

Defined in Foreign.C.Types

Storable CFloat 
Instance details

Defined in Foreign.C.Types

Storable CDouble 
Instance details

Defined in Foreign.C.Types

Storable CPtrdiff 
Instance details

Defined in Foreign.C.Types

Storable CSize 
Instance details

Defined in Foreign.C.Types

Storable CWchar 
Instance details

Defined in Foreign.C.Types

Storable CSigAtomic 
Instance details

Defined in Foreign.C.Types

Storable CClock 
Instance details

Defined in Foreign.C.Types

Storable CTime 
Instance details

Defined in Foreign.C.Types

Storable CUSeconds 
Instance details

Defined in Foreign.C.Types

Storable CSUSeconds 
Instance details

Defined in Foreign.C.Types

Storable CIntPtr 
Instance details

Defined in Foreign.C.Types

Storable CUIntPtr 
Instance details

Defined in Foreign.C.Types

Storable CIntMax 
Instance details

Defined in Foreign.C.Types

Storable CUIntMax 
Instance details

Defined in Foreign.C.Types

Storable Fingerprint

Since: base-4.4.0.0

Instance details

Defined in Foreign.Storable

Storable CTimeSpec 
Instance details

Defined in System.Posix.Files.Common

Methods

sizeOf :: CTimeSpec -> Int Source #

alignment :: CTimeSpec -> Int Source #

peekElemOff :: Ptr CTimeSpec -> Int -> IO CTimeSpec Source #

pokeElemOff :: Ptr CTimeSpec -> Int -> CTimeSpec -> IO () Source #

peekByteOff :: Ptr b -> Int -> IO CTimeSpec Source #

pokeByteOff :: Ptr b -> Int -> CTimeSpec -> IO () Source #

peek :: Ptr CTimeSpec -> IO CTimeSpec Source #

poke :: Ptr CTimeSpec -> CTimeSpec -> IO () Source #

Storable CTimeVal 
Instance details

Defined in System.Posix.Files.Common

Methods

sizeOf :: CTimeVal -> Int Source #

alignment :: CTimeVal -> Int Source #

peekElemOff :: Ptr CTimeVal -> Int -> IO CTimeVal Source #

pokeElemOff :: Ptr CTimeVal -> Int -> CTimeVal -> IO () Source #

peekByteOff :: Ptr b -> Int -> IO CTimeVal Source #

pokeByteOff :: Ptr b -> Int -> CTimeVal -> IO () Source #

peek :: Ptr CTimeVal -> IO CTimeVal Source #

poke :: Ptr CTimeVal -> CTimeVal -> IO () Source #

(Storable a, Integral a) => Storable (Ratio a)

Since: base-4.8.0.0

Instance details

Defined in Foreign.Storable

Methods

sizeOf :: Ratio a -> Int Source #

alignment :: Ratio a -> Int Source #

peekElemOff :: Ptr (Ratio a) -> Int -> IO (Ratio a) Source #

pokeElemOff :: Ptr (Ratio a) -> Int -> Ratio a -> IO () Source #

peekByteOff :: Ptr b -> Int -> IO (Ratio a) Source #

pokeByteOff :: Ptr b -> Int -> Ratio a -> IO () Source #

peek :: Ptr (Ratio a) -> IO (Ratio a) Source #

poke :: Ptr (Ratio a) -> Ratio a -> IO () Source #

Storable (StablePtr a)

Since: base-2.1

Instance details

Defined in Foreign.Storable

Storable (Ptr a)

Since: base-2.1

Instance details

Defined in Foreign.Storable

Methods

sizeOf :: Ptr a -> Int Source #

alignment :: Ptr a -> Int Source #

peekElemOff :: Ptr (Ptr a) -> Int -> IO (Ptr a) Source #

pokeElemOff :: Ptr (Ptr a) -> Int -> Ptr a -> IO () Source #

peekByteOff :: Ptr b -> Int -> IO (Ptr a) Source #

pokeByteOff :: Ptr b -> Int -> Ptr a -> IO () Source #

peek :: Ptr (Ptr a) -> IO (Ptr a) Source #

poke :: Ptr (Ptr a) -> Ptr a -> IO () Source #

Storable (FunPtr a)

Since: base-2.1

Instance details

Defined in Foreign.Storable

Methods

sizeOf :: FunPtr a -> Int Source #

alignment :: FunPtr a -> Int Source #

peekElemOff :: Ptr (FunPtr a) -> Int -> IO (FunPtr a) Source #

pokeElemOff :: Ptr (FunPtr a) -> Int -> FunPtr a -> IO () Source #

peekByteOff :: Ptr b -> Int -> IO (FunPtr a) Source #

pokeByteOff :: Ptr b -> Int -> FunPtr a -> IO () Source #

peek :: Ptr (FunPtr a) -> IO (FunPtr a) Source #

poke :: Ptr (FunPtr a) -> FunPtr a -> IO () Source #

plusPtr :: Ptr a -> Int -> Ptr b Source #

Advances the given address by the given offset in bytes.

nullPtr :: Ptr a Source #

The constant nullPtr contains a distinguished value of Ptr that is not associated with a valid memory location.

throwErrnoPathIfMinus1_ :: (Eq a, Num a) => String -> FilePath -> IO a -> IO () Source #

as throwErrnoIfMinus1_, but exceptions include the given path when appropriate.

throwErrnoIfNull :: String -> IO (Ptr a) -> IO (Ptr a) Source #

Throw an IOException corresponding to the current value of getErrno if the IO action returns nullPtr.

throwErrnoIfMinus1Retry_ :: (Eq a, Num a) => String -> IO a -> IO () Source #

as throwErrnoIfMinus1, but discards the result.

throwErrnoIfMinus1_ :: (Eq a, Num a) => String -> IO a -> IO () Source #

as throwErrnoIfMinus1, but discards the result.

withCWString :: String -> (CWString -> IO a) -> IO a Source #

Marshal a Haskell string into a NUL terminated C wide string using temporary storage.

  • the Haskell string may not contain any NUL characters
  • the memory is freed when the subcomputation terminates (either normally or via an exception), so the pointer to the temporary storage must not be used after this.

peekCWStringLen :: CWStringLen -> IO String Source #

Marshal a C wide string with explicit length into a Haskell string.

withCString :: String -> (CString -> IO a) -> IO a Source #

Marshal a Haskell string into a NUL terminated C string using temporary storage.

  • the Haskell string may not contain any NUL characters
  • the memory is freed when the subcomputation terminates (either normally or via an exception), so the pointer to the temporary storage must not be used after this.

peekCString :: CString -> IO String Source #

Marshal a NUL terminated C string into a Haskell string.

type CString = Ptr CChar Source #

A C string is a reference to an array of C characters terminated by NUL.

type CWString = Ptr CWchar Source #

A C wide string is a reference to an array of C wide characters terminated by NUL.

newtype CUChar Source #

Haskell type representing the C unsigned char type. (The concrete types of Foreign.C.Types are platform-specific.)

Constructors

CUChar Word8 

Instances

Instances details
Bounded CUChar 
Instance details

Defined in Foreign.C.Types

Enum CUChar 
Instance details

Defined in Foreign.C.Types

Eq CUChar 
Instance details

Defined in Foreign.C.Types

Methods

(==) :: CUChar -> CUChar -> Bool #

(/=) :: CUChar -> CUChar -> Bool #

Integral CUChar 
Instance details

Defined in Foreign.C.Types

Num CUChar 
Instance details

Defined in Foreign.C.Types

Ord CUChar 
Instance details

Defined in Foreign.C.Types

Read CUChar 
Instance details

Defined in Foreign.C.Types

Real CUChar 
Instance details

Defined in Foreign.C.Types

Show CUChar 
Instance details

Defined in Foreign.C.Types

Storable CUChar 
Instance details

Defined in Foreign.C.Types

Bits CUChar 
Instance details

Defined in Foreign.C.Types

FiniteBits CUChar 
Instance details

Defined in Foreign.C.Types

newtype CUShort Source #

Haskell type representing the C unsigned short type. (The concrete types of Foreign.C.Types are platform-specific.)

Constructors

CUShort Word16 

Instances

Instances details
Bounded CUShort 
Instance details

Defined in Foreign.C.Types

Enum CUShort 
Instance details

Defined in Foreign.C.Types

Eq CUShort 
Instance details

Defined in Foreign.C.Types

Methods

(==) :: CUShort -> CUShort -> Bool #

(/=) :: CUShort -> CUShort -> Bool #

Integral CUShort 
Instance details

Defined in Foreign.C.Types

Num CUShort 
Instance details

Defined in Foreign.C.Types

Ord CUShort 
Instance details

Defined in Foreign.C.Types

Read CUShort 
Instance details

Defined in Foreign.C.Types

Real CUShort 
Instance details

Defined in Foreign.C.Types

Show CUShort 
Instance details

Defined in Foreign.C.Types

Storable CUShort 
Instance details

Defined in Foreign.C.Types

Bits CUShort 
Instance details

Defined in Foreign.C.Types

FiniteBits CUShort 
Instance details

Defined in Foreign.C.Types

newtype CInt Source #

Haskell type representing the C int type. (The concrete types of Foreign.C.Types are platform-specific.)

Constructors

CInt Int32 

Instances

Instances details
Bounded CInt 
Instance details

Defined in Foreign.C.Types

Enum CInt 
Instance details

Defined in Foreign.C.Types

Eq CInt 
Instance details

Defined in Foreign.C.Types

Methods

(==) :: CInt -> CInt -> Bool #

(/=) :: CInt -> CInt -> Bool #

Integral CInt 
Instance details

Defined in Foreign.C.Types

Num CInt 
Instance details

Defined in Foreign.C.Types

Ord CInt 
Instance details

Defined in Foreign.C.Types

Methods

compare :: CInt -> CInt -> Ordering #

(<) :: CInt -> CInt -> Bool #

(<=) :: CInt -> CInt -> Bool #

(>) :: CInt -> CInt -> Bool #

(>=) :: CInt -> CInt -> Bool #

max :: CInt -> CInt -> CInt #

min :: CInt -> CInt -> CInt #

Read CInt 
Instance details

Defined in Foreign.C.Types

Real CInt 
Instance details

Defined in Foreign.C.Types

Show CInt 
Instance details

Defined in Foreign.C.Types

Storable CInt 
Instance details

Defined in Foreign.C.Types

Bits CInt 
Instance details

Defined in Foreign.C.Types

FiniteBits CInt 
Instance details

Defined in Foreign.C.Types

newtype CLong Source #

Haskell type representing the C long type. (The concrete types of Foreign.C.Types are platform-specific.)

Constructors

CLong Int64 

Instances

Instances details
Bounded CLong 
Instance details

Defined in Foreign.C.Types

Enum CLong 
Instance details

Defined in Foreign.C.Types

Eq CLong 
Instance details

Defined in Foreign.C.Types

Methods

(==) :: CLong -> CLong -> Bool #

(/=) :: CLong -> CLong -> Bool #

Integral CLong 
Instance details

Defined in Foreign.C.Types

Num CLong 
Instance details

Defined in Foreign.C.Types

Ord CLong 
Instance details

Defined in Foreign.C.Types

Methods

compare :: CLong -> CLong -> Ordering #

(<) :: CLong -> CLong -> Bool #

(<=) :: CLong -> CLong -> Bool #

(>) :: CLong -> CLong -> Bool #

(>=) :: CLong -> CLong -> Bool #

max :: CLong -> CLong -> CLong #

min :: CLong -> CLong -> CLong #

Read CLong 
Instance details

Defined in Foreign.C.Types

Real CLong 
Instance details

Defined in Foreign.C.Types

Show CLong 
Instance details

Defined in Foreign.C.Types

Storable CLong 
Instance details

Defined in Foreign.C.Types

Bits CLong 
Instance details

Defined in Foreign.C.Types

FiniteBits CLong 
Instance details

Defined in Foreign.C.Types

newtype CULong Source #

Haskell type representing the C unsigned long type. (The concrete types of Foreign.C.Types are platform-specific.)

Constructors

CULong Word64 

Instances

Instances details
Bounded CULong 
Instance details

Defined in Foreign.C.Types

Enum CULong 
Instance details

Defined in Foreign.C.Types

Eq CULong 
Instance details

Defined in Foreign.C.Types

Methods

(==) :: CULong -> CULong -> Bool #

(/=) :: CULong -> CULong -> Bool #

Integral CULong 
Instance details

Defined in Foreign.C.Types

Num CULong 
Instance details

Defined in Foreign.C.Types

Ord CULong 
Instance details

Defined in Foreign.C.Types

Read CULong 
Instance details

Defined in Foreign.C.Types

Real CULong 
Instance details

Defined in Foreign.C.Types

Show CULong 
Instance details

Defined in Foreign.C.Types

Storable CULong 
Instance details

Defined in Foreign.C.Types

Bits CULong 
Instance details

Defined in Foreign.C.Types

FiniteBits CULong 
Instance details

Defined in Foreign.C.Types

newtype CWchar Source #

Haskell type representing the C wchar_t type. (The concrete types of Foreign.C.Types are platform-specific.)

Constructors

CWchar Int32 

Instances

Instances details
Bounded CWchar 
Instance details

Defined in Foreign.C.Types

Enum CWchar 
Instance details

Defined in Foreign.C.Types

Eq CWchar 
Instance details

Defined in Foreign.C.Types

Methods

(==) :: CWchar -> CWchar -> Bool #

(/=) :: CWchar -> CWchar -> Bool #

Integral CWchar 
Instance details

Defined in Foreign.C.Types

Num CWchar 
Instance details

Defined in Foreign.C.Types

Ord CWchar 
Instance details

Defined in Foreign.C.Types

Read CWchar 
Instance details

Defined in Foreign.C.Types

Real CWchar 
Instance details

Defined in Foreign.C.Types

Show CWchar 
Instance details

Defined in Foreign.C.Types

Storable CWchar 
Instance details

Defined in Foreign.C.Types

Bits CWchar 
Instance details

Defined in Foreign.C.Types

FiniteBits CWchar 
Instance details

Defined in Foreign.C.Types

newtype CTime Source #

Haskell type representing the C time_t type. (The concrete types of Foreign.C.Types are platform-specific.)

Constructors

CTime Int64 

Instances

Instances details
Enum CTime 
Instance details

Defined in Foreign.C.Types

Eq CTime 
Instance details

Defined in Foreign.C.Types

Methods

(==) :: CTime -> CTime -> Bool #

(/=) :: CTime -> CTime -> Bool #

Num CTime 
Instance details

Defined in Foreign.C.Types

Ord CTime 
Instance details

Defined in Foreign.C.Types

Methods

compare :: CTime -> CTime -> Ordering #

(<) :: CTime -> CTime -> Bool #

(<=) :: CTime -> CTime -> Bool #

(>) :: CTime -> CTime -> Bool #

(>=) :: CTime -> CTime -> Bool #

max :: CTime -> CTime -> CTime #

min :: CTime -> CTime -> CTime #

Read CTime 
Instance details

Defined in Foreign.C.Types

Real CTime 
Instance details

Defined in Foreign.C.Types

Show CTime 
Instance details

Defined in Foreign.C.Types

Storable CTime 
Instance details

Defined in Foreign.C.Types

getFileSystemEncoding :: IO TextEncoding Source #

The Unicode encoding of the current locale, but allowing arbitrary undecodable bytes to be round-tripped through it.

This TextEncoding is used to decode and encode command line arguments and environment variables on non-Windows platforms.

On Windows, this encoding *should not* be used if possible because the use of code pages is deprecated: Strings should be retrieved via the "wide" W-family of UTF-16 APIs instead

Since: base-4.5.0.0

data IOErrorType Source #

An abstract type that contains a value for each variant of IOException.

Instances

Instances details
Eq IOErrorType

Since: base-4.1.0.0

Instance details

Defined in GHC.IO.Exception

Show IOErrorType

Since: base-4.1.0.0

Instance details

Defined in GHC.IO.Exception

lookupEnv :: String -> IO (Maybe String) Source #

Return the value of the environment variable var, or Nothing if there is no such value.

For POSIX users, this is equivalent to getEnv.

Since: base-4.6.0.0

getEnv :: String -> IO String Source #

Computation getEnv var returns the value of the environment variable var. For the inverse, the setEnv function can be used.

This computation may fail with:

getArgs :: IO [String] Source #

Computation getArgs returns a list of the program's command line arguments (not including the program name).

exitFailure :: IO a Source #

The computation exitFailure is equivalent to exitWith (ExitFailure exitfail), where exitfail is implementation-dependent.

openBinaryTempFile :: FilePath -> String -> IO (FilePath, Handle) Source #

Like openTempFile, but opens the file in binary mode. See openBinaryFile for more comments.

withBinaryFile :: FilePath -> IOMode -> (Handle -> IO r) -> IO r Source #

withBinaryFile name mode act opens a file using openBinaryFile and passes the resulting handle to the computation act. The handle will be closed on exit from withBinaryFile, whether by normal termination or by raising an exception.

hClose :: Handle -> IO () Source #

Computation hClose hdl makes handle hdl closed. Before the computation finishes, if hdl is writable its buffer is flushed as for hFlush. Performing hClose on a handle that has already been closed has no effect; doing so is not an error. All other operations on a closed handle will fail. If hClose fails for any reason, any further operations (apart from hClose) on the handle will still fail as if hdl had been successfully closed.

hGetBuf :: Handle -> Ptr a -> Int -> IO Int Source #

hGetBuf hdl buf count reads data from the handle hdl into the buffer buf until either EOF is reached or count 8-bit bytes have been read. It returns the number of bytes actually read. This may be zero if EOF was reached before any data was read (or if count is zero).

hGetBuf never raises an EOF exception, instead it returns a value smaller than count.

If the handle is a pipe or socket, and the writing end is closed, hGetBuf will behave as if EOF was reached.

hGetBuf ignores the prevailing TextEncoding and NewlineMode on the Handle, and reads bytes directly.

hPutBuf :: Handle -> Ptr a -> Int -> IO () Source #

hPutBuf hdl buf count writes count 8-bit bytes from the buffer buf to the handle hdl. It returns ().

hPutBuf ignores any text encoding that applies to the Handle, writing the bytes directly to the underlying file or device.

hPutBuf ignores the prevailing TextEncoding and NewlineMode on the Handle, and writes bytes directly.

This operation may fail with:

  • ResourceVanished if the handle is a pipe or socket, and the reading end is closed. (If this is a POSIX system, and the program has not asked to ignore SIGPIPE, then a SIGPIPE may be delivered instead, whose default action is to terminate the program).

hPutStrLn :: Handle -> String -> IO () Source #

The same as hPutStr, but adds a newline character.

hPutStr :: Handle -> String -> IO () Source #

Computation hPutStr hdl s writes the string s to the file or channel managed by hdl.

This operation may fail with:

hFlush :: Handle -> IO () Source #

The action hFlush hdl causes any items buffered for output in handle hdl to be sent immediately to the operating system.

This operation may fail with:

  • isFullError if the device is full;
  • isPermissionError if a system resource limit would be exceeded. It is unspecified whether the characters in the buffer are discarded or retained under these circumstances.

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.

Instances

Instances details
Eq Handle

Since: base-4.1.0.0

Instance details

Defined in GHC.IO.Handle.Types

Methods

(==) :: Handle -> Handle -> Bool #

(/=) :: Handle -> Handle -> Bool #

Show Handle

Since: base-4.1.0.0

Instance details

Defined in GHC.IO.Handle.Types

data IOMode Source #

Constructors

ReadMode 
WriteMode 

Instances

Instances details
Enum IOMode

Since: base-4.2.0.0

Instance details

Defined in GHC.IO.IOMode

Eq IOMode

Since: base-4.2.0.0

Instance details

Defined in GHC.IO.IOMode

Methods

(==) :: IOMode -> IOMode -> Bool #

(/=) :: IOMode -> IOMode -> Bool #

Ord IOMode

Since: base-4.2.0.0

Instance details

Defined in GHC.IO.IOMode

Read IOMode

Since: base-4.2.0.0

Instance details

Defined in GHC.IO.IOMode

Show IOMode

Since: base-4.2.0.0

Instance details

Defined in GHC.IO.IOMode

Ix IOMode

Since: base-4.2.0.0

Instance details

Defined in GHC.IO.IOMode

catchIOError :: IO a -> (IOError -> IO a) -> IO a Source #

The catchIOError function establishes a handler that receives any IOException raised in the action protected by catchIOError. An IOException is caught by the most recent handler established by one of the exception handling functions. These handlers are not selective: all IOExceptions are caught. Exception propagation must be explicitly provided in a handler by re-raising any unwanted exceptions. For example, in

f = catchIOError g (\e -> if IO.isEOFError e then return [] else ioError e)

the function f returns [] when an end-of-file exception (cf. isEOFError) occurs in g; otherwise, the exception is propagated to the next outer handler.

When an exception propagates outside the main program, the Haskell system prints the associated IOException value and exits the program.

Non-I/O exceptions are not caught by this variant; to catch all exceptions, use catch from Control.Exception.

Since: base-4.4.0.0

modifyIOError :: (IOError -> IOError) -> IO a -> IO a Source #

Catch any IOException that occurs in the computation and throw a modified version.

permissionErrorType :: IOErrorType Source #

I/O error where the operation failed because the user does not have sufficient operating system privilege to perform that operation.

illegalOperationErrorType :: IOErrorType Source #

I/O error where the operation is not possible.

isPermissionError :: IOError -> Bool Source #

An error indicating that an IO operation failed because the user does not have sufficient operating system privilege to perform that operation.

isIllegalOperation :: IOError -> Bool Source #

An error indicating that an IO operation failed because the operation was not possible. Any computation which returns an IO result may fail with isIllegalOperation. In some cases, an implementation will not be able to distinguish between the possible error causes. In this case it should fail with isIllegalOperation.

isDoesNotExistError :: IOError -> Bool Source #

An error indicating that an IO operation failed because one of its arguments does not exist.

isAlreadyExistsError :: IOError -> Bool Source #

An error indicating that an IO operation failed because one of its arguments already exists.

mkIOError :: IOErrorType -> String -> Maybe Handle -> Maybe FilePath -> IOError Source #

Construct an IOException of the given type where the second argument describes the error location and the third and fourth argument contain the file handle and file path of the file involved in the error if applicable.

tryIOError :: IO a -> IO (Either IOError a) Source #

The construct tryIOError comp exposes IO errors which occur within a computation, and which are not fully handled.

Non-I/O exceptions are not caught by this variant; to catch all exceptions, use try from Control.Exception.

Since: base-4.4.0.0

userError :: String -> IOError Source #

Construct an IOException value with a string describing the error. The fail method of the IO instance of the Monad class raises a userError, thus:

instance Monad IO where
  ...
  fail s = ioError (userError s)

type IOError = IOException Source #

The Haskell 2010 type for exceptions in the IO monad. Any I/O operation may raise an IOException instead of returning a result. For a more general type of exception, including also those that arise in pure code, see Exception.

In Haskell 2010, this is an opaque type.

timeout :: Int -> IO a -> IO (Maybe a) Source #

Wrap an IO computation to time out and return Nothing in case no result is available within n microseconds (1/10^6 seconds). In case a result is available before the timeout expires, Just a is returned. A negative timeout interval means "wait indefinitely". When specifying long timeouts, be careful not to exceed maxBound :: Int.

>>> timeout 1000000 (threadDelay 1000 *> pure "finished on time")
Just "finished on time"
>>> timeout 10000 (threadDelay 100000 *> pure "finished on time")
Nothing

The design of this combinator was guided by the objective that timeout n f should behave exactly the same as f as long as f doesn't time out. This means that f has the same myThreadId it would have without the timeout wrapper. Any exceptions f might throw cancel the timeout and propagate further up. It also possible for f to receive exceptions thrown to it by another thread.

A tricky implementation detail is the question of how to abort an IO computation. This combinator relies on asynchronous exceptions internally (namely throwing the computation the Timeout exception). The technique works very well for computations executing inside of the Haskell runtime system, but it doesn't work at all for non-Haskell code. Foreign function calls, for example, cannot be timed out with this combinator simply because an arbitrary C function cannot receive asynchronous exceptions. When timeout is used to wrap an FFI call that blocks, no timeout event can be delivered until the FFI call returns, which pretty much negates the purpose of the combinator. In practice, however, this limitation is less severe than it may sound. Standard I/O functions like hGetBuf, hPutBuf, Network.Socket.accept, or hWaitForInput appear to be blocking, but they really don't because the runtime system uses scheduling mechanisms like select(2) to perform asynchronous I/O, so it is possible to interrupt standard socket I/O or file I/O using this combinator.

data Void Source #

Uninhabited data type

Since: base-4.8.0.0

Instances

Instances details
Eq Void

Since: base-4.8.0.0

Instance details

Defined in Data.Void

Methods

(==) :: Void -> Void -> Bool #

(/=) :: Void -> Void -> Bool #

Data Void

Since: base-4.8.0.0

Instance details

Defined in Data.Void

Methods

gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> Void -> c Void Source #

gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c Void Source #

toConstr :: Void -> Constr Source #

dataTypeOf :: Void -> DataType Source #

dataCast1 :: Typeable t => (forall d. Data d => c (t d)) -> Maybe (c Void) Source #

dataCast2 :: Typeable t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c Void) Source #

gmapT :: (forall b. Data b => b -> b) -> Void -> Void Source #

gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> Void -> r Source #

gmapQr :: forall r r'. (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> Void -> r Source #

gmapQ :: (forall d. Data d => d -> u) -> Void -> [u] Source #

gmapQi :: Int -> (forall d. Data d => d -> u) -> Void -> u Source #

gmapM :: Monad m => (forall d. Data d => d -> m d) -> Void -> m Void Source #

gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> Void -> m Void Source #

gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> Void -> m Void Source #

Ord Void

Since: base-4.8.0.0

Instance details

Defined in Data.Void

Methods

compare :: Void -> Void -> Ordering #

(<) :: Void -> Void -> Bool #

(<=) :: Void -> Void -> Bool #

(>) :: Void -> Void -> Bool #

(>=) :: Void -> Void -> Bool #

max :: Void -> Void -> Void #

min :: Void -> Void -> Void #

Read Void

Reading a Void value is always a parse error, considering Void as a data type with no constructors.

Since: base-4.8.0.0

Instance details

Defined in Data.Void

Show Void

Since: base-4.8.0.0

Instance details

Defined in Data.Void

Ix Void

Since: base-4.8.0.0

Instance details

Defined in Data.Void

Generic Void 
Instance details

Defined in Data.Void

Associated Types

type Rep Void :: Type -> Type Source #

Methods

from :: Void -> Rep Void x Source #

to :: Rep Void x -> Void Source #

Semigroup Void

Since: base-4.9.0.0

Instance details

Defined in Data.Void

Exception Void

Since: base-4.8.0.0

Instance details

Defined in Data.Void

type Rep Void

Since: base-4.8.0.0

Instance details

Defined in Data.Void

type Rep Void = D1 ('MetaData "Void" "Data.Void" "base" 'False) (V1 :: Type -> Type)