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System.IO.Error

Portability | portable
Stability | provisional
Maintainer | libraries@haskell.org

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
ioeGetErrorString :: IOError -> String
ioeGetHandle :: IOError -> Maybe Handle
ioeGetFileName :: IOError -> Maybe FilePath
ioeSetErrorType :: IOError -> IOErrorType -> IOError
ioeSetErrorString :: 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
catch :: IO a -> (IOError -> IO a) -> IO a
try :: IO a -> IO (Either IOError a)
modifyIOError :: (IOError -> IOError) -> IO a -> IO a

I/O errors
type IOError = IOException
The Haskell 98 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 98, this is an opaque type.
userError :: String -> IOError

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
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
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
An error indicating that an `IO` operation failed because one of its arguments already exists.
isDoesNotExistError :: IOError -> Bool
An error indicating that an `IO` operation failed because one of its arguments does not exist.
isAlreadyInUseError :: IOError -> Bool
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
An error indicating that an `IO` operation failed because the device is full.
isEOFError :: IOError -> Bool
An error indicating that an `IO` operation failed because the end of file has been reached.
isIllegalOperation :: IOError -> Bool
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
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
A programmer-defined error value constructed using `userError`.
Attributes of I/O errors
ioeGetErrorType :: IOError -> IOErrorType
ioeGetErrorString :: IOError -> String
ioeGetHandle :: IOError -> Maybe Handle
ioeGetFileName :: IOError -> Maybe FilePath
ioeSetErrorType :: IOError -> IOErrorType -> IOError
ioeSetErrorString :: IOError -> String -> IOError
ioeSetHandle :: IOError -> Handle -> IOError
ioeSetFileName :: IOError -> FilePath -> IOError
Types of I/O error
data IOErrorType

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

Eq IOErrorType
Show IOErrorType

alreadyExistsErrorType :: IOErrorType
I/O error where the operation failed because one of its arguments already exists.
doesNotExistErrorType :: IOErrorType
I/O error where the operation failed because one of its arguments does not exist.
alreadyInUseErrorType :: IOErrorType
I/O error where the operation failed because one of its arguments is a single-use resource, which is already being used.
fullErrorType :: IOErrorType
I/O error where the operation failed because the device is full.
eofErrorType :: IOErrorType
I/O error where the operation failed because the end of file has been reached.
illegalOperationErrorType :: IOErrorType
I/O error where the operation is not possible.
permissionErrorType :: IOErrorType
I/O error where the operation failed because the user does not have sufficient operating system privilege to perform that operation.
userErrorType :: IOErrorType
I/O error that is programmer-defined.
`IOErrorType` predicates
isAlreadyExistsErrorType :: IOErrorType -> Bool
I/O error where the operation failed because one of its arguments already exists.
isDoesNotExistErrorType :: IOErrorType -> Bool
I/O error where the operation failed because one of its arguments does not exist.
isAlreadyInUseErrorType :: IOErrorType -> Bool
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
I/O error where the operation failed because the device is full.
isEOFErrorType :: IOErrorType -> Bool
I/O error where the operation failed because the end of file has been reached.
isIllegalOperationErrorType :: IOErrorType -> Bool
I/O error where the operation is not possible.
isPermissionErrorType :: IOErrorType -> Bool
I/O error where the operation failed because the user does not have sufficient operating system privilege to perform that operation.
isUserErrorType :: IOErrorType -> Bool
I/O error that is programmer-defined.
Throwing and catching I/O errors
ioError :: IOError -> IO a
Raise an `IOError` in the `IO` monad.
catch :: IO a -> (IOError -> IO a) -> IO a

The `catch` function establishes a handler that receives any `IOError` raised in the action protected by `catch`. An `IOError` is caught by the most recent handler established by `catch`. These handlers are not selective: all `IOError`s are caught. Exception propagation must be explicitly provided in a handler by re-raising any unwanted exceptions. For example, in

     f = catch 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.

try :: IO a -> IO (Either IOError a)
The construct `try` `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.
modifyIOError :: (IOError -> IOError) -> IO a -> IO a
Catch any `IOError` that occurs in the computation and throw a modified version.
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