Copyright	(c) The University of Glasgow 2001
License	BSD-style (see the file libraries/base/LICENSE)
Maintainer	libraries@haskell.org
Stability	provisional
Portability	portable
Safe Haskell	Trustworthy
Language	Haskell2010

System.IO.Error

Contents

I/O errors
- Classifying I/O errors
- Attributes of I/O errors
Types of I/O error
- IOErrorType predicates
Throwing and catching I/O errors

Description

Standard IO Errors.

Synopsis

type IOError = IOException
userError :: String -> IOError
mkIOError :: IOErrorType -> String -> Maybe Handle -> Maybe FilePath -> IOError
annotateIOError :: IOError -> String -> Maybe Handle -> Maybe FilePath -> IOError
isAlreadyExistsError :: IOError -> Bool
isDoesNotExistError :: IOError -> Bool
isAlreadyInUseError :: IOError -> Bool
isFullError :: IOError -> Bool
isEOFError :: IOError -> Bool
isIllegalOperation :: IOError -> Bool
isPermissionError :: IOError -> Bool
isUserError :: IOError -> Bool
ioeGetErrorType :: IOError -> IOErrorType
ioeGetLocation :: IOError -> String
ioeGetErrorString :: IOError -> String
ioeGetHandle :: IOError -> Maybe Handle
ioeGetFileName :: IOError -> Maybe FilePath
ioeSetErrorType :: IOError -> IOErrorType -> IOError
ioeSetErrorString :: IOError -> String -> IOError
ioeSetLocation :: IOError -> String -> IOError
ioeSetHandle :: IOError -> Handle -> IOError
ioeSetFileName :: IOError -> FilePath -> IOError
data IOErrorType
alreadyExistsErrorType :: IOErrorType
doesNotExistErrorType :: IOErrorType
alreadyInUseErrorType :: IOErrorType
fullErrorType :: IOErrorType
eofErrorType :: IOErrorType
illegalOperationErrorType :: IOErrorType
permissionErrorType :: IOErrorType
userErrorType :: IOErrorType
isAlreadyExistsErrorType :: IOErrorType -> Bool
isDoesNotExistErrorType :: IOErrorType -> Bool
isAlreadyInUseErrorType :: IOErrorType -> Bool
isFullErrorType :: IOErrorType -> Bool
isEOFErrorType :: IOErrorType -> Bool
isIllegalOperationErrorType :: IOErrorType -> Bool
isPermissionErrorType :: IOErrorType -> Bool
isUserErrorType :: IOErrorType -> Bool
ioError :: IOError -> IO a
catchIOError :: IO a -> (IOError -> IO a) -> IO a
tryIOError :: IO a -> IO (Either IOError a)
modifyIOError :: (IOError -> IOError) -> IO a -> IO a

I/O errors

type IOError = IOException Source #

The Haskell 2010 type for exceptions in the IO monad. Any I/O operation may raise an IOError 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.

userError :: String -> IOError Source #

Construct an IOError 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)

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

Construct an IOError 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.

annotateIOError :: IOError -> String -> Maybe Handle -> Maybe FilePath -> IOError Source #

Adds a location description and maybe a file path and file handle to an IOError. If any of the file handle or file path is not given the corresponding value in the IOError remains unaltered.

Classifying I/O errors

isAlreadyExistsError :: IOError -> Bool Source #

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

isDoesNotExistError :: IOError -> Bool Source #

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

isAlreadyInUseError :: IOError -> Bool Source #

An error indicating that an IO operation failed because one of its arguments is a single-use resource, which is already being used (for example, opening the same file twice for writing might give this error).

isFullError :: IOError -> Bool Source #

An error indicating that an IO operation failed because the device is full.

isEOFError :: IOError -> Bool Source #

An error indicating that an IO operation failed because the end of file has been reached.

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.

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.

isUserError :: IOError -> Bool Source #

A programmer-defined error value constructed using userError.

Attributes of I/O errors

ioeGetErrorType :: IOError -> IOErrorType Source #

ioeGetLocation :: IOError -> String Source #

ioeGetErrorString :: IOError -> String Source #

ioeGetHandle :: IOError -> Maybe Handle Source #

ioeGetFileName :: IOError -> Maybe FilePath Source #

ioeSetErrorType :: IOError -> IOErrorType -> IOError Source #

ioeSetErrorString :: IOError -> String -> IOError Source #

ioeSetLocation :: IOError -> String -> IOError Source #

ioeSetHandle :: IOError -> Handle -> IOError Source #

ioeSetFileName :: IOError -> FilePath -> IOError Source #

Types of I/O error

data IOErrorType Source #

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

Instances

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

alreadyExistsErrorType :: IOErrorType Source #

I/O error where the operation failed because one of its arguments already exists.

doesNotExistErrorType :: IOErrorType Source #

I/O error where the operation failed because one of its arguments does not exist.

alreadyInUseErrorType :: IOErrorType Source #

I/O error where the operation failed because one of its arguments is a single-use resource, which is already being used.

fullErrorType :: IOErrorType Source #

I/O error where the operation failed because the device is full.

eofErrorType :: IOErrorType Source #

I/O error where the operation failed because the end of file has been reached.

illegalOperationErrorType :: IOErrorType Source #

I/O error where the operation is not possible.

permissionErrorType :: IOErrorType Source #

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

userErrorType :: IOErrorType Source #

I/O error that is programmer-defined.

`IOErrorType` predicates

isAlreadyExistsErrorType :: IOErrorType -> Bool Source #

I/O error where the operation failed because one of its arguments already exists.

isDoesNotExistErrorType :: IOErrorType -> Bool Source #

I/O error where the operation failed because one of its arguments does not exist.

isAlreadyInUseErrorType :: IOErrorType -> Bool Source #

I/O error where the operation failed because one of its arguments is a single-use resource, which is already being used.

isFullErrorType :: IOErrorType -> Bool Source #

I/O error where the operation failed because the device is full.

isEOFErrorType :: IOErrorType -> Bool Source #

I/O error where the operation failed because the end of file has been reached.

isIllegalOperationErrorType :: IOErrorType -> Bool Source #

I/O error where the operation is not possible.

isPermissionErrorType :: IOErrorType -> Bool Source #

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

isUserErrorType :: IOErrorType -> Bool Source #

I/O error that is programmer-defined.

Throwing and catching I/O errors

ioError :: IOError -> IO a Source #

Raise an IOError in the IO monad.

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

The catchIOError function establishes a handler that receives any IOError raised in the action protected by catchIOError. An IOError is caught by the most recent handler established by one of the exception handling functions. These handlers are not selective: all IOErrors 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 IOError 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

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.