- class (Typeable e, Show e) => Exception e
- data LibCSPMException
- throwException :: Exception e => e -> a
- class Monad m => MonadIOException m where
- tryM :: MonadIOException m => m a -> m (Either LibCSPMException a)
- panic :: String -> a
- throwSourceError :: ErrorMessages -> a
- mkErrorMessage :: SrcSpan -> Doc -> ErrorMessage
- mkWarningMessage :: SrcSpan -> Doc -> ErrorMessage
- data ErrorMessage
- type ErrorMessages = [ErrorMessage]
Documentation
class (Typeable e, Show e) => Exception e
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 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 deriving Typeable 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 (Typeable, 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 MismatchedParenthesescatch
e -> putStrLn ("Caught " ++ show (e :: MismatchedParentheses)) Caught MismatchedParentheses *Main> throw MismatchedParenthesescatch
e -> putStrLn ("Caught " ++ show (e :: SomeFrontendException)) Caught MismatchedParentheses *Main> throw MismatchedParenthesescatch
e -> putStrLn ("Caught " ++ show (e :: SomeCompilerException)) Caught MismatchedParentheses *Main> throw MismatchedParenthesescatch
e -> putStrLn ("Caught " ++ show (e :: IOException)) *** Exception: MismatchedParentheses
data LibCSPMException Source
Exceptions that cause LibCSPM to abort whatever it is doing.
Panic String | An unexpected internal error |
SourceError ErrorMessages | An error in the user's input occured |
UserError | An error occured. Normally this is caught by the application and then turned into a SourceError. |
throwException :: Exception e => e -> aSource
Throws an arbitrary Exception
.
class Monad m => MonadIOException m whereSource
A class to allow catching of SourceErrors in arbitrary monads.
tryM :: MonadIOException m => m a -> m (Either LibCSPMException a)Source
MonadIOException IO | |
MonadIOException m => MonadIOException (StateT s m) |
throwSourceError :: ErrorMessages -> aSource
Throw an error message as a SourceError
.
mkErrorMessage :: SrcSpan -> Doc -> ErrorMessageSource
Given a SrcSpan
and a pretty printed Doc
creates an ErrorMessage
.
mkWarningMessage :: SrcSpan -> Doc -> ErrorMessageSource
data ErrorMessage Source
An error message that resulted from something in the user's input.
type ErrorMessages = [ErrorMessage]Source