    {-# LANGUAGE Trustworthy #-}
    {-# LANGUAGE DeriveGeneric, NoImplicitPrelude, MagicHash,
                 ExistentialQuantification, ImplicitParams #-}
    {-# OPTIONS_GHC -funbox-strict-fields #-}
    {-# OPTIONS_HADDOCK not-home #-}

    -----------------------------------------------------------------------------
    -- |
    -- Module      :  GHC.IO.Exception
    -- Copyright   :  (c) The University of Glasgow, 2009
    -- License     :  see libraries/base/LICENSE
    --
    -- Maintainer  :  libraries@haskell.org
    -- Stability   :  internal
    -- Portability :  non-portable
    --
    -- IO-related Exception types and functions
    --
    -----------------------------------------------------------------------------

    module GHC.IO.Exception (
      BlockedIndefinitelyOnMVar(..), blockedIndefinitelyOnMVar,
      BlockedIndefinitelyOnSTM(..), blockedIndefinitelyOnSTM,
      Deadlock(..),
      AllocationLimitExceeded(..), allocationLimitExceeded,
      AssertionFailed(..),
      CompactionFailed(..),
      cannotCompactFunction, cannotCompactPinned, cannotCompactMutable,

      SomeAsyncException(..),
      asyncExceptionToException, asyncExceptionFromException,
      AsyncException(..), stackOverflow, heapOverflow,

      ArrayException(..),
      ExitCode(..),
      FixIOException (..),

      ioException,
      ioError,
      IOError,
      IOException(..),
      IOErrorType(..),
      userError,
      assertError,
      unsupportedOperation,
      untangle,
     ) where

    import GHC.Base
    import GHC.Generics
    import GHC.List
    import GHC.IO
    import GHC.Show
    import GHC.Read
    import GHC.Exception
    import GHC.IO.Handle.Types
    import GHC.OldList ( intercalate )
    import {-# SOURCE #-} GHC.Stack.CCS
    import Foreign.C.Types

    import Data.Typeable ( cast )

    -- ------------------------------------------------------------------------
    -- Exception datatypes and operations

    -- |The thread is blocked on an @MVar@, but there are no other references
    -- to the @MVar@ so it can't ever continue.
    data BlockedIndefinitelyOnMVar = BlockedIndefinitelyOnMVar

    -- | @since 4.1.0.0
    instance Exception BlockedIndefinitelyOnMVar

    -- | @since 4.1.0.0
    instance Show BlockedIndefinitelyOnMVar where
        showsPrec :: Int -> BlockedIndefinitelyOnMVar -> ShowS
    showsPrec Int
    _ BlockedIndefinitelyOnMVar
    BlockedIndefinitelyOnMVar = String -> ShowS
    showString String
    "thread blocked indefinitely in an MVar operation"

    blockedIndefinitelyOnMVar :: SomeException -- for the RTS
    blockedIndefinitelyOnMVar :: SomeException
    blockedIndefinitelyOnMVar = BlockedIndefinitelyOnMVar -> SomeException
    forall e. Exception e => e -> SomeException
    toException BlockedIndefinitelyOnMVar
    BlockedIndefinitelyOnMVar

    -----

    -- |The thread is waiting to retry an STM transaction, but there are no
    -- other references to any @TVar@s involved, so it can't ever continue.
    data BlockedIndefinitelyOnSTM = BlockedIndefinitelyOnSTM

    -- | @since 4.1.0.0
    instance Exception BlockedIndefinitelyOnSTM

    -- | @since 4.1.0.0
    instance Show BlockedIndefinitelyOnSTM where
        showsPrec :: Int -> BlockedIndefinitelyOnSTM -> ShowS
    showsPrec Int
    _ BlockedIndefinitelyOnSTM
    BlockedIndefinitelyOnSTM = String -> ShowS
    showString String
    "thread blocked indefinitely in an STM transaction"

    blockedIndefinitelyOnSTM :: SomeException -- for the RTS
    blockedIndefinitelyOnSTM :: SomeException
    blockedIndefinitelyOnSTM = BlockedIndefinitelyOnSTM -> SomeException
    forall e. Exception e => e -> SomeException
    toException BlockedIndefinitelyOnSTM
    BlockedIndefinitelyOnSTM

    -----

    -- |There are no runnable threads, so the program is deadlocked.
    -- The @Deadlock@ exception is raised in the main thread only.
    data Deadlock = Deadlock

    -- | @since 4.1.0.0
    instance Exception Deadlock

    -- | @since 4.1.0.0
    instance Show Deadlock where
        showsPrec :: Int -> Deadlock -> ShowS
    showsPrec Int
    _ Deadlock
    Deadlock = String -> ShowS
    showString String
    "<<deadlock>>"

    -----

    -- |This thread has exceeded its allocation limit.  See
    -- 'System.Mem.setAllocationCounter' and
    -- 'System.Mem.enableAllocationLimit'.
    --
    -- @since 4.8.0.0
    data AllocationLimitExceeded = AllocationLimitExceeded

    -- | @since 4.8.0.0
    instance Exception AllocationLimitExceeded where
      toException :: AllocationLimitExceeded -> SomeException
    toException = AllocationLimitExceeded -> SomeException
    forall e. Exception e => e -> SomeException
    asyncExceptionToException
      fromException :: SomeException -> Maybe AllocationLimitExceeded
    fromException = SomeException -> Maybe AllocationLimitExceeded
    forall e. Exception e => SomeException -> Maybe e
    asyncExceptionFromException

    -- | @since 4.7.1.0
    instance Show AllocationLimitExceeded where
        showsPrec :: Int -> AllocationLimitExceeded -> ShowS
    showsPrec Int
    _ AllocationLimitExceeded
    AllocationLimitExceeded =
          String -> ShowS
    showString String
    "allocation limit exceeded"

    allocationLimitExceeded :: SomeException -- for the RTS
    allocationLimitExceeded :: SomeException
    allocationLimitExceeded = AllocationLimitExceeded -> SomeException
    forall e. Exception e => e -> SomeException
    toException AllocationLimitExceeded
    AllocationLimitExceeded

    -----

    -- | Compaction found an object that cannot be compacted.  Functions
    -- cannot be compacted, nor can mutable objects or pinned objects.
    -- See 'GHC.Compact.compact'.
    --
    -- @since 4.10.0.0
    newtype CompactionFailed = CompactionFailed String

    -- | @since 4.10.0.0
    instance Exception CompactionFailed where

    -- | @since 4.10.0.0
    instance Show CompactionFailed where
        showsPrec :: Int -> CompactionFailed -> ShowS
    showsPrec Int
    _ (CompactionFailed String
    why) =
          String -> ShowS
    showString (String
    "compaction failed: " String -> ShowS
    forall a. [a] -> [a] -> [a]
    ++ String
    why)

    cannotCompactFunction :: SomeException -- for the RTS
    cannotCompactFunction :: SomeException
    cannotCompactFunction =
      CompactionFailed -> SomeException
    forall e. Exception e => e -> SomeException
    toException (String -> CompactionFailed
    CompactionFailed String
    "cannot compact functions")

    cannotCompactPinned :: SomeException -- for the RTS
    cannotCompactPinned :: SomeException
    cannotCompactPinned =
      CompactionFailed -> SomeException
    forall e. Exception e => e -> SomeException
    toException (String -> CompactionFailed
    CompactionFailed String
    "cannot compact pinned objects")

    cannotCompactMutable :: SomeException -- for the RTS
    cannotCompactMutable :: SomeException
    cannotCompactMutable =
      CompactionFailed -> SomeException
    forall e. Exception e => e -> SomeException
    toException (String -> CompactionFailed
    CompactionFailed String
    "cannot compact mutable objects")

    -----

    -- |'assert' was applied to 'False'.
    newtype AssertionFailed = AssertionFailed String

    -- | @since 4.1.0.0
    instance Exception AssertionFailed

    -- | @since 4.1.0.0
    instance Show AssertionFailed where
        showsPrec :: Int -> AssertionFailed -> ShowS
    showsPrec Int
    _ (AssertionFailed String
    err) = String -> ShowS
    showString String
    err

    -----

    -- |Superclass for asynchronous exceptions.
    --
    -- @since 4.7.0.0
    data SomeAsyncException = forall e . Exception e => SomeAsyncException e

    -- | @since 4.7.0.0
    instance Show SomeAsyncException where
        showsPrec :: Int -> SomeAsyncException -> ShowS
    showsPrec Int
    p (SomeAsyncException e
    e) = Int -> e -> ShowS
    forall a. Show a => Int -> a -> ShowS
    showsPrec Int
    p e
    e

    -- | @since 4.7.0.0
    instance Exception SomeAsyncException

    -- |@since 4.7.0.0
    asyncExceptionToException :: Exception e => e -> SomeException
    asyncExceptionToException :: forall e. Exception e => e -> SomeException
    asyncExceptionToException = SomeAsyncException -> SomeException
    forall e. Exception e => e -> SomeException
    toException (SomeAsyncException -> SomeException)
    -> (e -> SomeAsyncException) -> e -> SomeException
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . e -> SomeAsyncException
    forall e. Exception e => e -> SomeAsyncException
    SomeAsyncException

    -- |@since 4.7.0.0
    asyncExceptionFromException :: Exception e => SomeException -> Maybe e
    asyncExceptionFromException :: forall e. Exception e => SomeException -> Maybe e
    asyncExceptionFromException SomeException
    x = do
        SomeAsyncException e
    a <- SomeException -> Maybe SomeAsyncException
    forall e. Exception e => SomeException -> Maybe e
    fromException SomeException
    x
        e -> Maybe e
    forall a b. (Typeable a, Typeable b) => a -> Maybe b
    cast e
    a

    -- |Asynchronous exceptions.
    data AsyncException
      = StackOverflow
            -- ^The current thread\'s stack exceeded its limit.
            -- Since an exception has been raised, the thread\'s stack
            -- will certainly be below its limit again, but the
            -- programmer should take remedial action
            -- immediately.
      | HeapOverflow
            -- ^The program\'s heap is reaching its limit, and
            -- the program should take action to reduce the amount of
            -- live data it has. Notes:
            --
            --   * It is undefined which thread receives this exception.
            --     GHC currently throws this to the same thread that
            --     receives 'UserInterrupt', but this may change in the
            --     future.
            --
            --   * The GHC RTS currently can only recover from heap overflow
            --     if it detects that an explicit memory limit (set via RTS flags).
            --     has been exceeded.  Currently, failure to allocate memory from
            --     the operating system results in immediate termination of the
            --     program.
      | ThreadKilled
            -- ^This exception is raised by another thread
            -- calling 'Control.Concurrent.killThread', or by the system
            -- if it needs to terminate the thread for some
            -- reason.
      | UserInterrupt
            -- ^This exception is raised by default in the main thread of
            -- the program when the user requests to terminate the program
            -- via the usual mechanism(s) (e.g. Control-C in the console).
      deriving ( AsyncException -> AsyncException -> Bool
    (AsyncException -> AsyncException -> Bool)
    -> (AsyncException -> AsyncException -> Bool) -> Eq AsyncException
    forall a. (a -> a -> Bool) -> (a -> a -> Bool) -> Eq a
    $c== :: AsyncException -> AsyncException -> Bool
    == :: AsyncException -> AsyncException -> Bool
    $c/= :: AsyncException -> AsyncException -> Bool
    /= :: AsyncException -> AsyncException -> Bool
    Eq  -- ^ @since 4.2.0.0
               , Eq AsyncException
    Eq AsyncException
    -> (AsyncException -> AsyncException -> Ordering)
    -> (AsyncException -> AsyncException -> Bool)
    -> (AsyncException -> AsyncException -> Bool)
    -> (AsyncException -> AsyncException -> Bool)
    -> (AsyncException -> AsyncException -> Bool)
    -> (AsyncException -> AsyncException -> AsyncException)
    -> (AsyncException -> AsyncException -> AsyncException)
    -> Ord AsyncException
    AsyncException -> AsyncException -> Bool
    AsyncException -> AsyncException -> Ordering
    AsyncException -> AsyncException -> AsyncException
    forall a.
    Eq a
    -> (a -> a -> Ordering)
    -> (a -> a -> Bool)
    -> (a -> a -> Bool)
    -> (a -> a -> Bool)
    -> (a -> a -> Bool)
    -> (a -> a -> a)
    -> (a -> a -> a)
    -> Ord a
    $ccompare :: AsyncException -> AsyncException -> Ordering
    compare :: AsyncException -> AsyncException -> Ordering
    $c< :: AsyncException -> AsyncException -> Bool
    < :: AsyncException -> AsyncException -> Bool
    $c<= :: AsyncException -> AsyncException -> Bool
    <= :: AsyncException -> AsyncException -> Bool
    $c> :: AsyncException -> AsyncException -> Bool
    > :: AsyncException -> AsyncException -> Bool
    $c>= :: AsyncException -> AsyncException -> Bool
    >= :: AsyncException -> AsyncException -> Bool
    $cmax :: AsyncException -> AsyncException -> AsyncException
    max :: AsyncException -> AsyncException -> AsyncException
    $cmin :: AsyncException -> AsyncException -> AsyncException
    min :: AsyncException -> AsyncException -> AsyncException
    Ord -- ^ @since 4.2.0.0
               )

    -- | @since 4.7.0.0
    instance Exception AsyncException where
      toException :: AsyncException -> SomeException
    toException = AsyncException -> SomeException
    forall e. Exception e => e -> SomeException
    asyncExceptionToException
      fromException :: SomeException -> Maybe AsyncException
    fromException = SomeException -> Maybe AsyncException
    forall e. Exception e => SomeException -> Maybe e
    asyncExceptionFromException

    -- | Exceptions generated by array operations
    data ArrayException
      = IndexOutOfBounds    String
            -- ^An attempt was made to index an array outside
            -- its declared bounds.
      | UndefinedElement    String
            -- ^An attempt was made to evaluate an element of an
            -- array that had not been initialized.
      deriving ( ArrayException -> ArrayException -> Bool
    (ArrayException -> ArrayException -> Bool)
    -> (ArrayException -> ArrayException -> Bool) -> Eq ArrayException
    forall a. (a -> a -> Bool) -> (a -> a -> Bool) -> Eq a
    $c== :: ArrayException -> ArrayException -> Bool
    == :: ArrayException -> ArrayException -> Bool
    $c/= :: ArrayException -> ArrayException -> Bool
    /= :: ArrayException -> ArrayException -> Bool
    Eq  -- ^ @since 4.2.0.0
               , Eq ArrayException
    Eq ArrayException
    -> (ArrayException -> ArrayException -> Ordering)
    -> (ArrayException -> ArrayException -> Bool)
    -> (ArrayException -> ArrayException -> Bool)
    -> (ArrayException -> ArrayException -> Bool)
    -> (ArrayException -> ArrayException -> Bool)
    -> (ArrayException -> ArrayException -> ArrayException)
    -> (ArrayException -> ArrayException -> ArrayException)
    -> Ord ArrayException
    ArrayException -> ArrayException -> Bool
    ArrayException -> ArrayException -> Ordering
    ArrayException -> ArrayException -> ArrayException
    forall a.
    Eq a
    -> (a -> a -> Ordering)
    -> (a -> a -> Bool)
    -> (a -> a -> Bool)
    -> (a -> a -> Bool)
    -> (a -> a -> Bool)
    -> (a -> a -> a)
    -> (a -> a -> a)
    -> Ord a
    $ccompare :: ArrayException -> ArrayException -> Ordering
    compare :: ArrayException -> ArrayException -> Ordering
    $c< :: ArrayException -> ArrayException -> Bool
    < :: ArrayException -> ArrayException -> Bool
    $c<= :: ArrayException -> ArrayException -> Bool
    <= :: ArrayException -> ArrayException -> Bool
    $c> :: ArrayException -> ArrayException -> Bool
    > :: ArrayException -> ArrayException -> Bool
    $c>= :: ArrayException -> ArrayException -> Bool
    >= :: ArrayException -> ArrayException -> Bool
    $cmax :: ArrayException -> ArrayException -> ArrayException
    max :: ArrayException -> ArrayException -> ArrayException
    $cmin :: ArrayException -> ArrayException -> ArrayException
    min :: ArrayException -> ArrayException -> ArrayException
    Ord -- ^ @since 4.2.0.0
               )

    -- | @since 4.1.0.0
    instance Exception ArrayException

    -- for the RTS
    stackOverflow, heapOverflow :: SomeException
    stackOverflow :: SomeException
    stackOverflow = AsyncException -> SomeException
    forall e. Exception e => e -> SomeException
    toException AsyncException
    StackOverflow
    heapOverflow :: SomeException
    heapOverflow  = AsyncException -> SomeException
    forall e. Exception e => e -> SomeException
    toException AsyncException
    HeapOverflow

    -- | @since 4.1.0.0
    instance Show AsyncException where
      showsPrec :: Int -> AsyncException -> ShowS
    showsPrec Int
    _ AsyncException
    StackOverflow   = String -> ShowS
    showString String
    "stack overflow"
      showsPrec Int
    _ AsyncException
    HeapOverflow    = String -> ShowS
    showString String
    "heap overflow"
      showsPrec Int
    _ AsyncException
    ThreadKilled    = String -> ShowS
    showString String
    "thread killed"
      showsPrec Int
    _ AsyncException
    UserInterrupt   = String -> ShowS
    showString String
    "user interrupt"

    -- | @since 4.1.0.0
    instance Show ArrayException where
      showsPrec :: Int -> ArrayException -> ShowS
    showsPrec Int
    _ (IndexOutOfBounds String
    s)
            = String -> ShowS
    showString String
    "array index out of range"
            ShowS -> ShowS -> ShowS
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . (if Bool -> Bool
    not (String -> Bool
    forall a. [a] -> Bool
    null String
    s) then String -> ShowS
    showString String
    ": " ShowS -> ShowS -> ShowS
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . String -> ShowS
    showString String
    s
                               else ShowS
    forall a. a -> a
    id)
      showsPrec Int
    _ (UndefinedElement String
    s)
            = String -> ShowS
    showString String
    "undefined array element"
            ShowS -> ShowS -> ShowS
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . (if Bool -> Bool
    not (String -> Bool
    forall a. [a] -> Bool
    null String
    s) then String -> ShowS
    showString String
    ": " ShowS -> ShowS -> ShowS
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . String -> ShowS
    showString String
    s
                               else ShowS
    forall a. a -> a
    id)

    -- | The exception thrown when an infinite cycle is detected in
    -- 'System.IO.fixIO'.
    --
    -- @since 4.11.0.0
    data FixIOException = FixIOException

    -- | @since 4.11.0.0
    instance Exception FixIOException

    -- | @since 4.11.0.0
    instance Show FixIOException where
      showsPrec :: Int -> FixIOException -> ShowS
    showsPrec Int
    _ FixIOException
    FixIOException = String -> ShowS
    showString String
    "cyclic evaluation in fixIO"

    -- -----------------------------------------------------------------------------
    -- The ExitCode type

    -- We need it here because it is used in ExitException in the
    -- Exception datatype (above).

    -- | Defines the exit codes that a program can return.
    data ExitCode
      = ExitSuccess -- ^ indicates successful termination;
      | ExitFailure Int
                    -- ^ indicates program failure with an exit code.
                    -- The exact interpretation of the code is
                    -- operating-system dependent.  In particular, some values
                    -- may be prohibited (e.g. 0 on a POSIX-compliant system).
      deriving (ExitCode -> ExitCode -> Bool
    (ExitCode -> ExitCode -> Bool)
    -> (ExitCode -> ExitCode -> Bool) -> Eq ExitCode
    forall a. (a -> a -> Bool) -> (a -> a -> Bool) -> Eq a
    $c== :: ExitCode -> ExitCode -> Bool
    == :: ExitCode -> ExitCode -> Bool
    $c/= :: ExitCode -> ExitCode -> Bool
    /= :: ExitCode -> ExitCode -> Bool
    Eq, Eq ExitCode
    Eq ExitCode
    -> (ExitCode -> ExitCode -> Ordering)
    -> (ExitCode -> ExitCode -> Bool)
    -> (ExitCode -> ExitCode -> Bool)
    -> (ExitCode -> ExitCode -> Bool)
    -> (ExitCode -> ExitCode -> Bool)
    -> (ExitCode -> ExitCode -> ExitCode)
    -> (ExitCode -> ExitCode -> ExitCode)
    -> Ord ExitCode
    ExitCode -> ExitCode -> Bool
    ExitCode -> ExitCode -> Ordering
    ExitCode -> ExitCode -> ExitCode
    forall a.
    Eq a
    -> (a -> a -> Ordering)
    -> (a -> a -> Bool)
    -> (a -> a -> Bool)
    -> (a -> a -> Bool)
    -> (a -> a -> Bool)
    -> (a -> a -> a)
    -> (a -> a -> a)
    -> Ord a
    $ccompare :: ExitCode -> ExitCode -> Ordering
    compare :: ExitCode -> ExitCode -> Ordering
    $c< :: ExitCode -> ExitCode -> Bool
    < :: ExitCode -> ExitCode -> Bool
    $c<= :: ExitCode -> ExitCode -> Bool
    <= :: ExitCode -> ExitCode -> Bool
    $c> :: ExitCode -> ExitCode -> Bool
    > :: ExitCode -> ExitCode -> Bool
    $c>= :: ExitCode -> ExitCode -> Bool
    >= :: ExitCode -> ExitCode -> Bool
    $cmax :: ExitCode -> ExitCode -> ExitCode
    max :: ExitCode -> ExitCode -> ExitCode
    $cmin :: ExitCode -> ExitCode -> ExitCode
    min :: ExitCode -> ExitCode -> ExitCode
    Ord, ReadPrec [ExitCode]
    ReadPrec ExitCode
    Int -> ReadS ExitCode
    ReadS [ExitCode]
    (Int -> ReadS ExitCode)
    -> ReadS [ExitCode]
    -> ReadPrec ExitCode
    -> ReadPrec [ExitCode]
    -> Read ExitCode
    forall a.
    (Int -> ReadS a)
    -> ReadS [a] -> ReadPrec a -> ReadPrec [a] -> Read a
    $creadsPrec :: Int -> ReadS ExitCode
    readsPrec :: Int -> ReadS ExitCode
    $creadList :: ReadS [ExitCode]
    readList :: ReadS [ExitCode]
    $creadPrec :: ReadPrec ExitCode
    readPrec :: ReadPrec ExitCode
    $creadListPrec :: ReadPrec [ExitCode]
    readListPrec :: ReadPrec [ExitCode]
    Read, Int -> ExitCode -> ShowS
    [ExitCode] -> ShowS
    ExitCode -> String
    (Int -> ExitCode -> ShowS)
    -> (ExitCode -> String) -> ([ExitCode] -> ShowS) -> Show ExitCode
    forall a.
    (Int -> a -> ShowS) -> (a -> String) -> ([a] -> ShowS) -> Show a
    $cshowsPrec :: Int -> ExitCode -> ShowS
    showsPrec :: Int -> ExitCode -> ShowS
    $cshow :: ExitCode -> String
    show :: ExitCode -> String
    $cshowList :: [ExitCode] -> ShowS
    showList :: [ExitCode] -> ShowS
    Show, (forall x. ExitCode -> Rep ExitCode x)
    -> (forall x. Rep ExitCode x -> ExitCode) -> Generic ExitCode
    forall x. Rep ExitCode x -> ExitCode
    forall x. ExitCode -> Rep ExitCode x
    forall a.
    (forall x. a -> Rep a x) -> (forall x. Rep a x -> a) -> Generic a
    $cfrom :: forall x. ExitCode -> Rep ExitCode x
    from :: forall x. ExitCode -> Rep ExitCode x
    $cto :: forall x. Rep ExitCode x -> ExitCode
    to :: forall x. Rep ExitCode x -> ExitCode
    Generic)

    -- | @since 4.1.0.0
    instance Exception ExitCode

    ioException     :: IOException -> IO a
    ioException :: forall a. IOException -> IO a
    ioException IOException
    err = IOException -> IO a
    forall e a. Exception e => e -> IO a
    throwIO IOException
    err

    -- | Raise an 'IOError' in the 'IO' monad.
    ioError         :: IOError -> IO a
    ioError :: forall a. IOException -> IO a
    ioError         =  IOException -> IO a
    forall a. IOException -> IO a
    ioException

    -- ---------------------------------------------------------------------------
    -- IOError type

    -- | 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 'Control.Exception.Exception'.
    --
    -- In Haskell 2010, this is an opaque type.
    type IOError = IOException

    -- |Exceptions that occur in the @IO@ monad.
    -- An @IOException@ records a more specific error type, a descriptive
    -- string and maybe the handle that was used when the error was
    -- flagged.
    data IOException
     = IOError {
         IOException -> Maybe Handle
    ioe_handle   :: Maybe Handle,   -- the handle used by the action flagging
                                         -- the error.
         IOException -> IOErrorType
    ioe_type     :: IOErrorType,    -- what it was.
         IOException -> String
    ioe_location :: String,         -- location.
         IOException -> String
    ioe_description :: String,      -- error type specific information.
         IOException -> Maybe CInt
    ioe_errno    :: Maybe CInt,     -- errno leading to this error, if any.
         IOException -> Maybe String
    ioe_filename :: Maybe FilePath  -- filename the error is related to.
       }

    -- | @since 4.1.0.0
    instance Exception IOException

    -- | @since 4.1.0.0
    instance Eq IOException where
      (IOError Maybe Handle
    h1 IOErrorType
    e1 String
    loc1 String
    str1 Maybe CInt
    en1 Maybe String
    fn1) == :: IOException -> IOException -> Bool
    == (IOError Maybe Handle
    h2 IOErrorType
    e2 String
    loc2 String
    str2 Maybe CInt
    en2 Maybe String
    fn2) =
        IOErrorType
    e1IOErrorType -> IOErrorType -> Bool
    forall a. Eq a => a -> a -> Bool
    ==IOErrorType
    e2 Bool -> Bool -> Bool
    && String
    str1String -> String -> Bool
    forall a. Eq a => a -> a -> Bool
    ==String
    str2 Bool -> Bool -> Bool
    && Maybe Handle
    h1Maybe Handle -> Maybe Handle -> Bool
    forall a. Eq a => a -> a -> Bool
    ==Maybe Handle
    h2 Bool -> Bool -> Bool
    && String
    loc1String -> String -> Bool
    forall a. Eq a => a -> a -> Bool
    ==String
    loc2 Bool -> Bool -> Bool
    && Maybe CInt
    en1Maybe CInt -> Maybe CInt -> Bool
    forall a. Eq a => a -> a -> Bool
    ==Maybe CInt
    en2 Bool -> Bool -> Bool
    && Maybe String
    fn1Maybe String -> Maybe String -> Bool
    forall a. Eq a => a -> a -> Bool
    ==Maybe String
    fn2

    -- | An abstract type that contains a value for each variant of 'IOError'.
    data IOErrorType
      -- Haskell 2010:
      = AlreadyExists
      | NoSuchThing
      | ResourceBusy
      | ResourceExhausted
      | EOF
      | IllegalOperation
      | PermissionDenied
      | UserError
      -- GHC only:
      | UnsatisfiedConstraints
      | SystemError
      | ProtocolError
      | OtherError
      | InvalidArgument
      | InappropriateType
      | HardwareFault
      | UnsupportedOperation
      | TimeExpired
      | ResourceVanished
      | Interrupted

    -- | @since 4.1.0.0
    instance Eq IOErrorType where
       IOErrorType
    x == :: IOErrorType -> IOErrorType -> Bool
    == IOErrorType
    y = Int# -> Bool
    isTrue# (IOErrorType -> Int#
    forall a. a -> Int#
    getTag IOErrorType
    x Int# -> Int# -> Int#
    ==# IOErrorType -> Int#
    forall a. a -> Int#
    getTag IOErrorType
    y)

    -- | @since 4.1.0.0
    instance Show IOErrorType where
      showsPrec :: Int -> IOErrorType -> ShowS
    showsPrec Int
    _ IOErrorType
    e =
        String -> ShowS
    showString (String -> ShowS) -> String -> ShowS
    forall a b. (a -> b) -> a -> b
    $
        case IOErrorType
    e of
          IOErrorType
    AlreadyExists     -> String
    "already exists"
          IOErrorType
    NoSuchThing       -> String
    "does not exist"
          IOErrorType
    ResourceBusy      -> String
    "resource busy"
          IOErrorType
    ResourceExhausted -> String
    "resource exhausted"
          IOErrorType
    EOF               -> String
    "end of file"
          IOErrorType
    IllegalOperation  -> String
    "illegal operation"
          IOErrorType
    PermissionDenied  -> String
    "permission denied"
          IOErrorType
    UserError         -> String
    "user error"
          IOErrorType
    HardwareFault     -> String
    "hardware fault"
          IOErrorType
    InappropriateType -> String
    "inappropriate type"
          IOErrorType
    Interrupted       -> String
    "interrupted"
          IOErrorType
    InvalidArgument   -> String
    "invalid argument"
          IOErrorType
    OtherError        -> String
    "failed"
          IOErrorType
    ProtocolError     -> String
    "protocol error"
          IOErrorType
    ResourceVanished  -> String
    "resource vanished"
          IOErrorType
    SystemError       -> String
    "system error"
          IOErrorType
    TimeExpired       -> String
    "timeout"
          IOErrorType
    UnsatisfiedConstraints -> String
    "unsatisfied constraints" -- ultra-precise!
          IOErrorType
    UnsupportedOperation -> String
    "unsupported operation"

    -- | 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)
    --
    userError       :: String  -> IOError
    userError :: String -> IOException
    userError String
    str   =  Maybe Handle
    -> IOErrorType
    -> String
    -> String
    -> Maybe CInt
    -> Maybe String
    -> IOException
    IOError Maybe Handle
    forall a. Maybe a
    Nothing IOErrorType
    UserError String
    "" String
    str Maybe CInt
    forall a. Maybe a
    Nothing Maybe String
    forall a. Maybe a
    Nothing

    -- ---------------------------------------------------------------------------
    -- Showing IOErrors

    -- | @since 4.1.0.0
    instance Show IOException where
        showsPrec :: Int -> IOException -> ShowS
    showsPrec Int
    p (IOError Maybe Handle
    hdl IOErrorType
    iot String
    loc String
    s Maybe CInt
    _ Maybe String
    fn) =
          (case Maybe String
    fn of
             Maybe String
    Nothing -> case Maybe Handle
    hdl of
                            Maybe Handle
    Nothing -> ShowS
    forall a. a -> a
    id
                            Just Handle
    h  -> Int -> Handle -> ShowS
    forall a. Show a => Int -> a -> ShowS
    showsPrec Int
    p Handle
    h ShowS -> ShowS -> ShowS
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . String -> ShowS
    showString String
    ": "
             Just String
    name -> String -> ShowS
    showString String
    name ShowS -> ShowS -> ShowS
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . String -> ShowS
    showString String
    ": ") ShowS -> ShowS -> ShowS
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    .
          (case String
    loc of
             String
    "" -> ShowS
    forall a. a -> a
    id
             String
    _  -> String -> ShowS
    showString String
    loc ShowS -> ShowS -> ShowS
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . String -> ShowS
    showString String
    ": ") ShowS -> ShowS -> ShowS
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    .
          Int -> IOErrorType -> ShowS
    forall a. Show a => Int -> a -> ShowS
    showsPrec Int
    p IOErrorType
    iot ShowS -> ShowS -> ShowS
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    .
          (case String
    s of
             String
    "" -> ShowS
    forall a. a -> a
    id
             String
    _  -> String -> ShowS
    showString String
    " (" ShowS -> ShowS -> ShowS
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . String -> ShowS
    showString String
    s ShowS -> ShowS -> ShowS
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . String -> ShowS
    showString String
    ")")

    -- Note the use of "lazy". This means that
    --     assert False (throw e)
    -- will throw the assertion failure rather than e. See trac #5561.
    assertError :: (?callStack :: CallStack) => Bool -> a -> a
    assertError :: forall a. (?callStack::CallStack) => Bool -> a -> a
    assertError Bool
    predicate a
    v
      | Bool
    predicate = a -> a
    forall a. a -> a
    lazy a
    v
      | Bool
    otherwise = IO a -> a
    forall a. IO a -> a
    unsafeDupablePerformIO (IO a -> a) -> IO a -> a
    forall a b. (a -> b) -> a -> b
    $ do
        [String]
    ccsStack <- IO [String]
    currentCallStack
        let
          implicitParamCallStack :: [String]
    implicitParamCallStack = CallStack -> [String]
    prettyCallStackLines ?callStack::CallStack
    CallStack
    ?callStack
          ccsCallStack :: [String]
    ccsCallStack = [String] -> [String]
    showCCSStack [String]
    ccsStack
          stack :: String
    stack = String -> [String] -> String
    forall a. [a] -> [[a]] -> [a]
    intercalate String
    "\n" ([String] -> String) -> [String] -> String
    forall a b. (a -> b) -> a -> b
    $ [String]
    implicitParamCallStack [String] -> [String] -> [String]
    forall a. [a] -> [a] -> [a]
    ++ [String]
    ccsCallStack
        AssertionFailed -> IO a
    forall e a. Exception e => e -> IO a
    throwIO (String -> AssertionFailed
    AssertionFailed (String
    "Assertion failed\n" String -> ShowS
    forall a. [a] -> [a] -> [a]
    ++ String
    stack))

    unsupportedOperation :: IOError
    unsupportedOperation :: IOException
    unsupportedOperation =
       (Maybe Handle
    -> IOErrorType
    -> String
    -> String
    -> Maybe CInt
    -> Maybe String
    -> IOException
    IOError Maybe Handle
    forall a. Maybe a
    Nothing IOErrorType
    UnsupportedOperation String
    ""
            String
    "Operation is not supported" Maybe CInt
    forall a. Maybe a
    Nothing Maybe String
    forall a. Maybe a
    Nothing)

    {-
    (untangle coded message) expects "coded" to be of the form
            "location|details"
    It prints
            location message details
    -}
    untangle :: Addr# -> String -> String
    untangle :: Addr# -> ShowS
    untangle Addr#
    coded String
    message
      =  String
    location
      String -> ShowS
    forall a. [a] -> [a] -> [a]
    ++ String
    ": "
      String -> ShowS
    forall a. [a] -> [a] -> [a]
    ++ String
    message
      String -> ShowS
    forall a. [a] -> [a] -> [a]
    ++ String
    details
      String -> ShowS
    forall a. [a] -> [a] -> [a]
    ++ String
    "\n"
      where
        coded_str :: String
    coded_str = Addr# -> String
    unpackCStringUtf8# Addr#
    coded

        (String
    location, String
    details)
          = case ((Char -> Bool) -> String -> (String, String)
    forall a. (a -> Bool) -> [a] -> ([a], [a])
    span Char -> Bool
    not_bar String
    coded_str) of { (String
    loc, String
    rest) ->
            case String
    rest of
              (Char
    '|':String
    det) -> (String
    loc, Char
    ' ' Char -> ShowS
    forall a. a -> [a] -> [a]
    : String
    det)
              String
    _         -> (String
    loc, String
    "")
            }
        not_bar :: Char -> Bool
    not_bar Char
    c = Char
    c Char -> Char -> Bool
    forall a. Eq a => a -> a -> Bool
    /= Char
    '|'