- type IOError = IOError
- 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
- ioeGetErrorString :: IOError -> String
- ioeGetHandle :: IOError -> Maybe Handle
- ioeGetFileName :: IOError -> Maybe FilePath
- data IOErrorType
- alreadyExistsErrorType :: IOErrorType
- doesNotExistErrorType :: IOErrorType
- alreadyInUseErrorType :: IOErrorType
- fullErrorType :: IOErrorType
- eofErrorType :: IOErrorType
- illegalOperationErrorType :: IOErrorType
- permissionErrorType :: IOErrorType
- userErrorType :: IOErrorType
- ioError :: IOError -> IO a
- catch :: IO a -> (IOError -> IO a) -> IO a
- try :: IO a -> IO (Either IOError a)
I/O errors
Errors of type IOError
are used by the IO
monad. This is an
abstract type; the module System.IO.Error provides functions to
interrogate and construct values of type IOError
.
mkIOError :: IOErrorType -> String -> Maybe Handle -> Maybe FilePath -> IOErrorSource
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.
Classifying I/O errors
isAlreadyExistsError :: IOError -> BoolSource
An error indicating that an IO
operation failed because
one of its arguments already exists.
isDoesNotExistError :: IOError -> BoolSource
An error indicating that an IO
operation failed because
one of its arguments does not exist.
isAlreadyInUseError :: IOError -> BoolSource
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 -> BoolSource
An error indicating that an IO
operation failed because
the device is full.
isEOFError :: IOError -> BoolSource
An error indicating that an IO
operation failed because
the end of file has been reached.
isIllegalOperation :: IOError -> BoolSource
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 -> BoolSource
An error indicating that an IO
operation failed because
the user does not have sufficient operating system privilege
to perform that operation.
isUserError :: IOError -> BoolSource
A programmer-defined error value constructed using userError
.
Attributes of I/O errors
ioeGetHandle :: IOError -> Maybe HandleSource
Types of I/O error
data IOErrorType Source
An abstract type that contains a value for each variant of IOError
.
alreadyExistsErrorType :: IOErrorTypeSource
I/O error where the operation failed because one of its arguments already exists.
doesNotExistErrorType :: IOErrorTypeSource
I/O error where the operation failed because one of its arguments does not exist.
alreadyInUseErrorType :: IOErrorTypeSource
I/O error where the operation failed because one of its arguments is a single-use resource, which is already being used.
fullErrorType :: IOErrorTypeSource
I/O error where the operation failed because the device is full.
eofErrorType :: IOErrorTypeSource
I/O error where the operation failed because the end of file has been reached.
illegalOperationErrorType :: IOErrorTypeSource
I/O error where the operation is not possible.
permissionErrorType :: IOErrorTypeSource
I/O error where the operation failed because the user does not have sufficient operating system privilege to perform that operation.
userErrorType :: IOErrorTypeSource
I/O error that is programmer-defined.
Throwing and catching I/O errors
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.