Copyright | (c) 2016 Stephen Diehl (c) 2016-2018 Serokell (c) 2018-2023 Kowainik |
---|---|
License | MIT |
Maintainer | Kowainik <xrom.xkov@gmail.com> |
Stability | Stable |
Portability | Portable |
Safe Haskell | Safe |
Language | Haskell2010 |
- Control.Exception reexports
Bug
s
Re-exports most useful functionality from the Control.Exception module. Also provides some convenient utilities to throw and handle exceptions.
Synopsis
- class (Typeable e, Show e) => Exception e where
- toException :: e -> SomeException
- fromException :: SomeException -> Maybe e
- displayException :: e -> String
- backtraceDesired :: e -> Bool
- data SomeException = (Exception e, HasExceptionContext) => SomeException e
- data Bug = Bug SomeException CallStack
- bug :: (HasCallStack, Exception e) => e -> a
- pattern Exc :: Exception e => e -> SomeException
Control.Exception reexports
class (Typeable e, Show e) => Exception e where #
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
Nothing
toException :: e -> SomeException #
toException
should produce a SomeException
with no attached ExceptionContext
.
fromException :: SomeException -> Maybe e #
displayException :: e -> String #
Render this exception value in a human-friendly manner.
Default implementation:
.show
@since base-4.8.0.0
backtraceDesired :: e -> Bool #
Instances
data SomeException #
The SomeException
type is the root of the exception type hierarchy.
When an exception of type e
is thrown, behind the scenes it is
encapsulated in a SomeException
.
(Exception e, HasExceptionContext) => SomeException e |
Instances
Exception SomeException | This drops any attached @since base-3.0 |
Defined in GHC.Internal.Exception.Type | |
Show SomeException | Since: ghc-internal-3.0 |
Defined in GHC.Internal.Exception.Type showsPrec :: Int -> SomeException -> ShowS # show :: SomeException -> String # showList :: [SomeException] -> ShowS # |
Bug
s
Type that represents exceptions used in cases when a particular codepath is not meant to be ever executed, but happens to be executed anyway.
Instances
Exception Bug Source # | |
Defined in Relude.Exception toException :: Bug -> SomeException # fromException :: SomeException -> Maybe Bug # displayException :: Bug -> String # backtraceDesired :: Bug -> Bool # | |
Show Bug Source # | |
bug :: (HasCallStack, Exception e) => e -> a Source #
Generate a pure value which, when forced, will synchronously
throw the exception wrapped into Bug
data type.
pattern Exc :: Exception e => e -> SomeException Source #
Pattern synonym to easy pattern matching on exceptions. So instead of writing something like this:
isNonCriticalExc :: SomeException -> Bool isNonCriticalExc e | Just (_ :: NodeAttackedError) <- fromException e = True | Just DialogUnexpected{} <- fromException e = True | otherwise = False
you can use Exc
pattern synonym:
isNonCriticalExc :: SomeException -> Bool isNonCriticalExc = case Exc (_ :: NodeAttackedError) -> True -- matching all exceptions of type NodeAttackedError Exc DialogUnexpected{} -> True _ -> False
This pattern is bidirectional. You can use Exc e
instead of toException e
.