| Safe Haskell | None |
|---|---|
| Language | Haskell2010 |
Servant.Exception
Synopsis
- data Throws (e :: Type)
- class (Typeable e, Show e) => ToServantErr e where
- data ServantException
- toServantException :: (Exception e, ToJSON e, ToServantErr e) => e -> SomeException
- fromServantException :: Exception e => SomeException -> Maybe e
- class (Typeable e, Show e) => Exception e where
- toException :: e -> SomeException
- fromException :: SomeException -> Maybe e
- displayException :: e -> String
- mapException :: (Exception e1, Exception e2, MonadCatch m) => (e1 -> e2) -> m a -> m a
Documentation
class (Typeable e, Show e) => ToServantErr e where Source #
Minimal complete definition
Instances
| ToServantErr ServantException Source # | |
Defined in Servant.Exception Methods status :: ServantException -> Status Source # message :: ServantException -> Text Source # headers :: ServantException -> [Header] Source # | |
data ServantException Source #
A root exception type (see Control.Exception) to provide a common
rendering format via MimeRender for builtin content types JSON and
PlainText.
Instances
| Show ServantException Source # | |
Defined in Servant.Exception Methods showsPrec :: Int -> ServantException -> ShowS # show :: ServantException -> String # showList :: [ServantException] -> ShowS # | |
| Exception ServantException Source # | |
Defined in Servant.Exception Methods toException :: ServantException -> SomeException # | |
| ToServantErr ServantException Source # | |
Defined in Servant.Exception Methods status :: ServantException -> Status Source # message :: ServantException -> Text Source # headers :: ServantException -> [Header] Source # | |
| MimeRender JSON ServantException Source # | |
Defined in Servant.Exception Methods mimeRender :: Proxy JSON -> ServantException -> ByteString # | |
| MimeRender PlainText ServantException Source # | |
Defined in Servant.Exception Methods mimeRender :: Proxy PlainText -> ServantException -> ByteString # | |
toServantException :: (Exception e, ToJSON e, ToServantErr e) => e -> SomeException Source #
fromServantException :: Exception e => SomeException -> Maybe e Source #
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 MyExceptionThe 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 = frontendExceptionFromExceptionWe 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
Minimal complete definition
Nothing
Methods
toException :: e -> SomeException #
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
Instances
mapException :: (Exception e1, Exception e2, MonadCatch m) => (e1 -> e2) -> m a -> m a Source #
Catch and rethrow using mapping function f.