base-4.3.1.0: Basic libraries

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

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
- 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 Source

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 Control.Exception.Exception.

In Haskell 98, 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 |
Show IOErrorType |

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 aSource

Raise an `IOError` in the `IO` monad.

catch :: IO a -> (IOError -> IO a) -> IO aSource

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 `Control.Exception.catch` from Control.Exception.

try :: IO a -> IO (Either IOError a)Source

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 `Control.Exception.try` from Control.Exception.

modifyIOError :: (IOError -> IOError) -> IO a -> IO aSource

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