module GHC.Exception where import Data.Maybe import Data.Typeable (Typeable, cast) import GHC.Base import GHC.Show\end{code} %********************************************************* %* * \subsection{Exceptions} %* * %********************************************************* \begin{code}
data SomeException = forall e . Exception e => SomeException e
deriving Typeable
instance Show SomeException where
showsPrec p (SomeException e) = showsPrec p e
class (Typeable e, Show e) => Exception e where
toException :: e -> SomeException
fromException :: SomeException -> Maybe e
toException = SomeException
fromException (SomeException e) = cast e
instance Exception SomeException where
toException se = se
fromException = Just
\end{code} %********************************************************* %* * \subsection{Primitive throw} %* * %********************************************************* \begin{code}
throw :: Exception e => e -> a throw e = raise# (toException e)\end{code} \begin{code}
data ErrorCall = ErrorCall String
deriving Typeable
instance Exception ErrorCall
instance Show ErrorCall where
showsPrec _ (ErrorCall err) = showString err
data ArithException
= Overflow
| Underflow
| LossOfPrecision
| DivideByZero
| Denormal
deriving (Eq, Ord, Typeable)
instance Exception ArithException
instance Show ArithException where
showsPrec _ Overflow = showString "arithmetic overflow"
showsPrec _ Underflow = showString "arithmetic underflow"
showsPrec _ LossOfPrecision = showString "loss of precision"
showsPrec _ DivideByZero = showString "divide by zero"
showsPrec _ Denormal = showString "denormal"
\end{code}
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