Exception +Control

module Control.Exception
base 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.
class (Typeable e, Show e) => Exception e
base Control.Exception.Base, base 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, Typeable) > > 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 > deriving Typeable > > instance Show SomeCompilerException > 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 > deriving Typeable > > instance Show SomeFrontendException > show (SomeFrontendException e) = show e > > instance Exception SomeFrontendException > 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 (Typeable, Show) > > instance Exception MismatchedParentheses > 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
data Exception
base Control.OldException
The type of exceptions. Every kind of system-generated exception has a constructor in the Exception type, and values of other types may be injected into Exception by coercing them to Dynamic (see the section on Dynamic Exceptions: Control.OldException#DynamicExceptions).
package exception-mailer
package
This module is designed to be used in production code when no runtime exceptions are expected.  This module will catch any unexpected runtime exception and send a notification email Version 0.3
package exception-monads-fd
package
This package provides exception monad transformer instances for the classes defined by monads-fd. Version 0.2
package exception-monads-tf
package
This package provides exception monad transformer instances for the classes defined by monads-tf. Version 0.3.0.2
package exception-mtl
package
This package provides exception monad transformer instances for the classes defined by mtl2. Version 0.3.0.3
package exception-transformers
package
This package provides type classes, a monad and a monad transformer that support unchecked extensible exceptions as well as asynchronous exceptions. It is compatible with the transformers package. Version 0.3.0.3
package exceptions
package
Extensible optionally-pure exceptions Version 0.3.2
ArithException :: ArithException -> Exception
base Control.OldException
Exceptions raised by arithmetic operations. (NOTE: GHC currently does not throw ArithExceptions except for DivideByZero).
data ArithException
base Control.Exception.Base, base Control.Exception, base Control.OldException
Arithmetic exceptions.
arithExceptions :: Exception -> Maybe ArithException
base Control.OldException
ArrayException :: ArrayException -> Exception
base Control.OldException
Exceptions raised by array-related operations. (NOTE: GHC currently does not throw ArrayExceptions).
data ArrayException
base Control.Exception.Base, base Control.Exception, base Control.OldException
Exceptions generated by array operations
AsyncException :: AsyncException -> Exception
base Control.OldException
Asynchronous exceptions (see section on Asynchronous Exceptions: Control.OldException#AsynchronousExceptions).
data AsyncException
base Control.Exception.Base, base Control.Exception, base Control.OldException
Asynchronous exceptions.
asyncExceptions :: Exception -> Maybe AsyncException
base Control.OldException
module Control.OldException
base Control.OldException
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.
DynException :: Dynamic -> Exception
base Control.OldException
Dynamically typed exceptions (see section on Dynamic Exceptions: Control.OldException#DynamicExceptions).
dynExceptions :: Exception -> Maybe Dynamic
base Control.OldException

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