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1. module GHC.Internal.Control.Exception

   This module provides support for raising and catching both built-in and user-defined exceptions. In addition to exceptions thrown by IO operations, exceptions may be thrown by pure code (imprecise exceptions) or by external events (asynchronous exceptions), but may only be caught in the IO monad. For more details, see:

   • A semantics for imprecise exceptions, by Simon Peyton Jones, Alastair Reid, Tony Hoare, Simon Marlow, Fergus Henderson, in PLDI'99.
   • Asynchronous exceptions in Haskell, by Simon Marlow, Simon Peyton Jones, Andy Moran and John Reppy, in PLDI'01.
   • An Extensible Dynamically-Typed Hierarchy of Exceptions, by Simon Marlow, in Haskell '06.

2. class (Typeable e, Show e) => Exception e

   ghc-internal	GHC.Internal.Control.Exception

   Any type that you wish to throw or catch as an exception must be an instance of the Exception class. The simplest case is a new exception type directly below the root:

   data MyException = ThisException | ThatException
   deriving Show
   
   instance Exception MyException
   

   The default method definitions in the Exception class do what we need in this case. You can now throw and catch ThisException and ThatException as exceptions:

   *Main> throw ThisException `catch` \e -> putStrLn ("Caught " ++ show (e :: MyException))
   Caught ThisException
   

   In more complicated examples, you may wish to define a whole hierarchy of exceptions:

   ---------------------------------------------------------------------
   -- Make the root exception type for all the exceptions in a compiler
   
   data SomeCompilerException = forall e . Exception e => SomeCompilerException e
   
   instance Show SomeCompilerException where
   show (SomeCompilerException e) = show e
   
   instance Exception SomeCompilerException
   
   compilerExceptionToException :: Exception e => e -> SomeException
   compilerExceptionToException = toException . SomeCompilerException
   
   compilerExceptionFromException :: Exception e => SomeException -> Maybe e
   compilerExceptionFromException x = do
   SomeCompilerException a <- fromException x
   cast a
   
   ---------------------------------------------------------------------
   -- Make a subhierarchy for exceptions in the frontend of the compiler
   
   data SomeFrontendException = forall e . Exception e => SomeFrontendException e
   
   instance Show SomeFrontendException where
   show (SomeFrontendException e) = show e
   
   instance Exception SomeFrontendException where
   toException = compilerExceptionToException
   fromException = compilerExceptionFromException
   
   frontendExceptionToException :: Exception e => e -> SomeException
   frontendExceptionToException = toException . SomeFrontendException
   
   frontendExceptionFromException :: Exception e => SomeException -> Maybe e
   frontendExceptionFromException x = do
   SomeFrontendException a <- fromException x
   cast a
   
   ---------------------------------------------------------------------
   -- Make an exception type for a particular frontend compiler exception
   
   data MismatchedParentheses = MismatchedParentheses
   deriving Show
   
   instance Exception MismatchedParentheses where
   toException   = frontendExceptionToException
   fromException = frontendExceptionFromException
   

   We can now catch a MismatchedParentheses exception as MismatchedParentheses, SomeFrontendException or SomeCompilerException, but not other types, e.g. IOException:

   *Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: MismatchedParentheses))
   Caught MismatchedParentheses
   *Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: SomeFrontendException))
   Caught MismatchedParentheses
   *Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: SomeCompilerException))
   Caught MismatchedParentheses
   *Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: IOException))
   *** Exception: MismatchedParentheses
   

3. class (Typeable e, Show e) => Exception e

   ghc-internal	GHC.Internal.Control.Exception.Base

   Any type that you wish to throw or catch as an exception must be an instance of the Exception class. The simplest case is a new exception type directly below the root:

   data MyException = ThisException | ThatException
   deriving Show
   
   instance Exception MyException
   

   The default method definitions in the Exception class do what we need in this case. You can now throw and catch ThisException and ThatException as exceptions:

   *Main> throw ThisException `catch` \e -> putStrLn ("Caught " ++ show (e :: MyException))
   Caught ThisException
   

   In more complicated examples, you may wish to define a whole hierarchy of exceptions:

   ---------------------------------------------------------------------
   -- Make the root exception type for all the exceptions in a compiler
   
   data SomeCompilerException = forall e . Exception e => SomeCompilerException e
   
   instance Show SomeCompilerException where
   show (SomeCompilerException e) = show e
   
   instance Exception SomeCompilerException
   
   compilerExceptionToException :: Exception e => e -> SomeException
   compilerExceptionToException = toException . SomeCompilerException
   
   compilerExceptionFromException :: Exception e => SomeException -> Maybe e
   compilerExceptionFromException x = do
   SomeCompilerException a <- fromException x
   cast a
   
   ---------------------------------------------------------------------
   -- Make a subhierarchy for exceptions in the frontend of the compiler
   
   data SomeFrontendException = forall e . Exception e => SomeFrontendException e
   
   instance Show SomeFrontendException where
   show (SomeFrontendException e) = show e
   
   instance Exception SomeFrontendException where
   toException = compilerExceptionToException
   fromException = compilerExceptionFromException
   
   frontendExceptionToException :: Exception e => e -> SomeException
   frontendExceptionToException = toException . SomeFrontendException
   
   frontendExceptionFromException :: Exception e => SomeException -> Maybe e
   frontendExceptionFromException x = do
   SomeFrontendException a <- fromException x
   cast a
   
   ---------------------------------------------------------------------
   -- Make an exception type for a particular frontend compiler exception
   
   data MismatchedParentheses = MismatchedParentheses
   deriving Show
   
   instance Exception MismatchedParentheses where
   toException   = frontendExceptionToException
   fromException = frontendExceptionFromException
   

   We can now catch a MismatchedParentheses exception as MismatchedParentheses, SomeFrontendException or SomeCompilerException, but not other types, e.g. IOException:

   *Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: MismatchedParentheses))
   Caught MismatchedParentheses
   *Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: SomeFrontendException))
   Caught MismatchedParentheses
   *Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: SomeCompilerException))
   Caught MismatchedParentheses
   *Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: IOException))
   *** Exception: MismatchedParentheses
   

4. module TextShow.Control.Exception

   TextShow instances for Exception data types. Since: 2

5. module Control.Monad.Exception

   No documentation available.

6. class (Typeable e, Show e) => Exception e

   exception-transformers	Control.Monad.Exception

   Any type that you wish to throw or catch as an exception must be an instance of the Exception class. The simplest case is a new exception type directly below the root:

   data MyException = ThisException | ThatException
   deriving Show
   
   instance Exception MyException
   

   The default method definitions in the Exception class do what we need in this case. You can now throw and catch ThisException and ThatException as exceptions:

   *Main> throw ThisException `catch` \e -> putStrLn ("Caught " ++ show (e :: MyException))
   Caught ThisException
   

   In more complicated examples, you may wish to define a whole hierarchy of exceptions:

   ---------------------------------------------------------------------
   -- Make the root exception type for all the exceptions in a compiler
   
   data SomeCompilerException = forall e . Exception e => SomeCompilerException e
   
   instance Show SomeCompilerException where
   show (SomeCompilerException e) = show e
   
   instance Exception SomeCompilerException
   
   compilerExceptionToException :: Exception e => e -> SomeException
   compilerExceptionToException = toException . SomeCompilerException
   
   compilerExceptionFromException :: Exception e => SomeException -> Maybe e
   compilerExceptionFromException x = do
   SomeCompilerException a <- fromException x
   cast a
   
   ---------------------------------------------------------------------
   -- Make a subhierarchy for exceptions in the frontend of the compiler
   
   data SomeFrontendException = forall e . Exception e => SomeFrontendException e
   
   instance Show SomeFrontendException where
   show (SomeFrontendException e) = show e
   
   instance Exception SomeFrontendException where
   toException = compilerExceptionToException
   fromException = compilerExceptionFromException
   
   frontendExceptionToException :: Exception e => e -> SomeException
   frontendExceptionToException = toException . SomeFrontendException
   
   frontendExceptionFromException :: Exception e => SomeException -> Maybe e
   frontendExceptionFromException x = do
   SomeFrontendException a <- fromException x
   cast a
   
   ---------------------------------------------------------------------
   -- Make an exception type for a particular frontend compiler exception
   
   data MismatchedParentheses = MismatchedParentheses
   deriving Show
   
   instance Exception MismatchedParentheses where
   toException   = frontendExceptionToException
   fromException = frontendExceptionFromException
   

   We can now catch a MismatchedParentheses exception as MismatchedParentheses, SomeFrontendException or SomeCompilerException, but not other types, e.g. IOException:

   *Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: MismatchedParentheses))
   Caught MismatchedParentheses
   *Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: SomeFrontendException))
   Caught MismatchedParentheses
   *Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: SomeCompilerException))
   Caught MismatchedParentheses
   *Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: IOException))
   *** Exception: MismatchedParentheses
   

7. module Rebase.Control.Exception

   No documentation available.

8. class (Typeable e, Show e) => Exception e

   annotated-exception	Control.Exception.Annotated

   Any type that you wish to throw or catch as an exception must be an instance of the Exception class. The simplest case is a new exception type directly below the root:

   data MyException = ThisException | ThatException
   deriving Show
   
   instance Exception MyException
   

   The default method definitions in the Exception class do what we need in this case. You can now throw and catch ThisException and ThatException as exceptions:

   *Main> throw ThisException `catch` \e -> putStrLn ("Caught " ++ show (e :: MyException))
   Caught ThisException
   

   In more complicated examples, you may wish to define a whole hierarchy of exceptions:

   ---------------------------------------------------------------------
   -- Make the root exception type for all the exceptions in a compiler
   
   data SomeCompilerException = forall e . Exception e => SomeCompilerException e
   
   instance Show SomeCompilerException where
   show (SomeCompilerException e) = show e
   
   instance Exception SomeCompilerException
   
   compilerExceptionToException :: Exception e => e -> SomeException
   compilerExceptionToException = toException . SomeCompilerException
   
   compilerExceptionFromException :: Exception e => SomeException -> Maybe e
   compilerExceptionFromException x = do
   SomeCompilerException a <- fromException x
   cast a
   
   ---------------------------------------------------------------------
   -- Make a subhierarchy for exceptions in the frontend of the compiler
   
   data SomeFrontendException = forall e . Exception e => SomeFrontendException e
   
   instance Show SomeFrontendException where
   show (SomeFrontendException e) = show e
   
   instance Exception SomeFrontendException where
   toException = compilerExceptionToException
   fromException = compilerExceptionFromException
   
   frontendExceptionToException :: Exception e => e -> SomeException
   frontendExceptionToException = toException . SomeFrontendException
   
   frontendExceptionFromException :: Exception e => SomeException -> Maybe e
   frontendExceptionFromException x = do
   SomeFrontendException a <- fromException x
   cast a
   
   ---------------------------------------------------------------------
   -- Make an exception type for a particular frontend compiler exception
   
   data MismatchedParentheses = MismatchedParentheses
   deriving Show
   
   instance Exception MismatchedParentheses where
   toException   = frontendExceptionToException
   fromException = frontendExceptionFromException
   

   We can now catch a MismatchedParentheses exception as MismatchedParentheses, SomeFrontendException or SomeCompilerException, but not other types, e.g. IOException:

   *Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: MismatchedParentheses))
   Caught MismatchedParentheses
   *Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: SomeFrontendException))
   Caught MismatchedParentheses
   *Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: SomeCompilerException))
   Caught MismatchedParentheses
   *Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: IOException))
   *** Exception: MismatchedParentheses
   

9. class (Typeable e, Show e) => Exception e

   annotated-exception	Control.Exception.Annotated.UnliftIO

   Any type that you wish to throw or catch as an exception must be an instance of the Exception class. The simplest case is a new exception type directly below the root:

   data MyException = ThisException | ThatException
   deriving Show
   
   instance Exception MyException
   

   The default method definitions in the Exception class do what we need in this case. You can now throw and catch ThisException and ThatException as exceptions:

   *Main> throw ThisException `catch` \e -> putStrLn ("Caught " ++ show (e :: MyException))
   Caught ThisException
   

   In more complicated examples, you may wish to define a whole hierarchy of exceptions:

   ---------------------------------------------------------------------
   -- Make the root exception type for all the exceptions in a compiler
   
   data SomeCompilerException = forall e . Exception e => SomeCompilerException e
   
   instance Show SomeCompilerException where
   show (SomeCompilerException e) = show e
   
   instance Exception SomeCompilerException
   
   compilerExceptionToException :: Exception e => e -> SomeException
   compilerExceptionToException = toException . SomeCompilerException
   
   compilerExceptionFromException :: Exception e => SomeException -> Maybe e
   compilerExceptionFromException x = do
   SomeCompilerException a <- fromException x
   cast a
   
   ---------------------------------------------------------------------
   -- Make a subhierarchy for exceptions in the frontend of the compiler
   
   data SomeFrontendException = forall e . Exception e => SomeFrontendException e
   
   instance Show SomeFrontendException where
   show (SomeFrontendException e) = show e
   
   instance Exception SomeFrontendException where
   toException = compilerExceptionToException
   fromException = compilerExceptionFromException
   
   frontendExceptionToException :: Exception e => e -> SomeException
   frontendExceptionToException = toException . SomeFrontendException
   
   frontendExceptionFromException :: Exception e => SomeException -> Maybe e
   frontendExceptionFromException x = do
   SomeFrontendException a <- fromException x
   cast a
   
   ---------------------------------------------------------------------
   -- Make an exception type for a particular frontend compiler exception
   
   data MismatchedParentheses = MismatchedParentheses
   deriving Show
   
   instance Exception MismatchedParentheses where
   toException   = frontendExceptionToException
   fromException = frontendExceptionFromException
   

   We can now catch a MismatchedParentheses exception as MismatchedParentheses, SomeFrontendException or SomeCompilerException, but not other types, e.g. IOException:

   *Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: MismatchedParentheses))
   Caught MismatchedParentheses
   *Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: SomeFrontendException))
   Caught MismatchedParentheses
   *Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: SomeCompilerException))
   Caught MismatchedParentheses
   *Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: IOException))
   *** Exception: MismatchedParentheses
   

10. class (Typeable e, Show e) => Exception e

    monad-peel	Control.Exception.Peel

    Any type that you wish to throw or catch as an exception must be an instance of the Exception class. The simplest case is a new exception type directly below the root:

    data MyException = ThisException | ThatException
    deriving Show
    
    instance Exception MyException
    

    The default method definitions in the Exception class do what we need in this case. You can now throw and catch ThisException and ThatException as exceptions:

    *Main> throw ThisException `catch` \e -> putStrLn ("Caught " ++ show (e :: MyException))
    Caught ThisException
    

    In more complicated examples, you may wish to define a whole hierarchy of exceptions:

    ---------------------------------------------------------------------
    -- Make the root exception type for all the exceptions in a compiler
    
    data SomeCompilerException = forall e . Exception e => SomeCompilerException e
    
    instance Show SomeCompilerException where
    show (SomeCompilerException e) = show e
    
    instance Exception SomeCompilerException
    
    compilerExceptionToException :: Exception e => e -> SomeException
    compilerExceptionToException = toException . SomeCompilerException
    
    compilerExceptionFromException :: Exception e => SomeException -> Maybe e
    compilerExceptionFromException x = do
    SomeCompilerException a <- fromException x
    cast a
    
    ---------------------------------------------------------------------
    -- Make a subhierarchy for exceptions in the frontend of the compiler
    
    data SomeFrontendException = forall e . Exception e => SomeFrontendException e
    
    instance Show SomeFrontendException where
    show (SomeFrontendException e) = show e
    
    instance Exception SomeFrontendException where
    toException = compilerExceptionToException
    fromException = compilerExceptionFromException
    
    frontendExceptionToException :: Exception e => e -> SomeException
    frontendExceptionToException = toException . SomeFrontendException
    
    frontendExceptionFromException :: Exception e => SomeException -> Maybe e
    frontendExceptionFromException x = do
    SomeFrontendException a <- fromException x
    cast a
    
    ---------------------------------------------------------------------
    -- Make an exception type for a particular frontend compiler exception
    
    data MismatchedParentheses = MismatchedParentheses
    deriving Show
    
    instance Exception MismatchedParentheses where
    toException   = frontendExceptionToException
    fromException = frontendExceptionFromException
    

    We can now catch a MismatchedParentheses exception as MismatchedParentheses, SomeFrontendException or SomeCompilerException, but not other types, e.g. IOException:

    *Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: MismatchedParentheses))
    Caught MismatchedParentheses
    *Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: SomeFrontendException))
    Caught MismatchedParentheses
    *Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: SomeCompilerException))
    Caught MismatchedParentheses
    *Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: IOException))
    *** Exception: MismatchedParentheses
    

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