explicit-exception-0.1.5: Exceptions which are explicit in the type signature.Source codeContentsIndex
Control.Monad.Exception.Synchronous
Description

Synchronous exceptions immediately abort a series of computations. We provide monads for describing this behaviour. In contrast to ErrorT from mtl or transformers package we do not pose restrictions on the exception type.

How to tell, that a function can possibly throw more than one (kind of) exception?

If you would use the exception type (Either ParserException IOError) then this is different from (Either IOError ParserException). Thus we recommned using type classes for exceptions. Then you can use one type containing all exceptions in an application, but the type signature still tells which exceptions are actually possible. Examples:

 parser :: ParserException e => ExceptionalT e ParserMonad a

 getLine :: IOException e => ExceptionalT e IO String

 fileParser :: (ParserException e, IOException e) => ExceptionalT e IO String

Unfortunately, this way you cannot remove single exceptions from the constraints by catching them. You can only remove all of them using resolve or none. For a more advanced approach, that allows removing exceptions constraints by some non-Haskell-98 type hackery, see the exception package by Joseph Iborra.

Synopsis
data Exceptional e a
= Success a
| Exception e
fromMaybe :: e -> Maybe a -> Exceptional e a
toMaybe :: Exceptional e a -> Maybe a
fromEither :: Either e a -> Exceptional e a
toEither :: Exceptional e a -> Either e a
getExceptionNull :: Exceptional e () -> Maybe e
switch :: (e -> b) -> (a -> b) -> Exceptional e a -> b
force :: Exceptional e a -> Exceptional e a
mapException :: (e0 -> e1) -> Exceptional e0 a -> Exceptional e1 a
mapExceptional :: (e0 -> e1) -> (a -> b) -> Exceptional e0 a -> Exceptional e1 b
throw :: e -> Exceptional e a
assert :: e -> Bool -> Exceptional e ()
catch :: Exceptional e0 a -> (e0 -> Exceptional e1 a) -> Exceptional e1 a
resolve :: (e -> a) -> Exceptional e a -> a
newtype ExceptionalT e m a = ExceptionalT {
runExceptionalT :: m (Exceptional e a)
}
fromErrorT :: Monad m => ErrorT e m a -> ExceptionalT e m a
toErrorT :: Monad m => ExceptionalT e m a -> ErrorT e m a
fromEitherT :: Monad m => m (Either e a) -> ExceptionalT e m a
toEitherT :: Monad m => ExceptionalT e m a -> m (Either e a)
forceT :: Monad m => ExceptionalT e m a -> ExceptionalT e m a
mapExceptionT :: Monad m => (e0 -> e1) -> ExceptionalT e0 m a -> ExceptionalT e1 m a
mapExceptionalT :: (m (Exceptional e0 a) -> n (Exceptional e1 b)) -> ExceptionalT e0 m a -> ExceptionalT e1 n b
throwT :: Monad m => e -> ExceptionalT e m a
assertT :: Monad m => e -> Bool -> ExceptionalT e m ()
catchT :: Monad m => ExceptionalT e0 m a -> (e0 -> ExceptionalT e1 m a) -> ExceptionalT e1 m a
bracketT :: Monad m => ExceptionalT e m h -> (h -> ExceptionalT e m ()) -> (h -> ExceptionalT e m a) -> ExceptionalT e m a
resolveT :: Monad m => (e -> m a) -> ExceptionalT e m a -> m a
tryT :: Monad m => ExceptionalT e m a -> m (Exceptional e a)
manyT :: Monad m => (e0 -> Maybe e1) -> (a -> b -> b) -> b -> ExceptionalT e0 m a -> ExceptionalT e1 m b
manyMonoidT :: (Monad m, Monoid a) => (e0 -> Maybe e1) -> ExceptionalT e0 m a -> ExceptionalT e1 m a
Documentation
data Exceptional e a Source
Like Either, but explicitly intended for handling of exceptional results. In contrast to Either we do not support fail. Calling fail in the Exceptional monad is an error. This way, we do not require that an exception can be derived from a String, yet, we require no constraint on the exception type at all.
Constructors
Success a
Exception e
fromMaybe :: e -> Maybe a -> Exceptional e aSource
toMaybe :: Exceptional e a -> Maybe aSource
fromEither :: Either e a -> Exceptional e aSource
toEither :: Exceptional e a -> Either e aSource
getExceptionNull :: Exceptional e () -> Maybe eSource
useful in connection with Control.Monad.Exception.Asynchronous.continue
switch :: (e -> b) -> (a -> b) -> Exceptional e a -> bSource
Counterpart to either for Either.
force :: Exceptional e a -> Exceptional e aSource
If you are sure that the value is always a Success you can tell that the run-time system thus making your program lazy. However, try to avoid this function by using catch and friends, since this function is partial.
mapException :: (e0 -> e1) -> Exceptional e0 a -> Exceptional e1 aSource
mapExceptional :: (e0 -> e1) -> (a -> b) -> Exceptional e0 a -> Exceptional e1 bSource
throw :: e -> Exceptional e aSource
assert :: e -> Bool -> Exceptional e ()Source
catch :: Exceptional e0 a -> (e0 -> Exceptional e1 a) -> Exceptional e1 aSource
resolve :: (e -> a) -> Exceptional e a -> aSource
newtype ExceptionalT e m a Source
like ErrorT, but ExceptionalT is the better name in order to distinguish from real (programming) errors
Constructors
ExceptionalT
runExceptionalT :: m (Exceptional e a)
fromErrorT :: Monad m => ErrorT e m a -> ExceptionalT e m aSource
toErrorT :: Monad m => ExceptionalT e m a -> ErrorT e m aSource
fromEitherT :: Monad m => m (Either e a) -> ExceptionalT e m aSource
toEitherT :: Monad m => ExceptionalT e m a -> m (Either e a)Source
forceT :: Monad m => ExceptionalT e m a -> ExceptionalT e m aSource
see force
mapExceptionT :: Monad m => (e0 -> e1) -> ExceptionalT e0 m a -> ExceptionalT e1 m aSource
mapExceptionalT :: (m (Exceptional e0 a) -> n (Exceptional e1 b)) -> ExceptionalT e0 m a -> ExceptionalT e1 n bSource
throwT :: Monad m => e -> ExceptionalT e m aSource
assertT :: Monad m => e -> Bool -> ExceptionalT e m ()Source
catchT :: Monad m => ExceptionalT e0 m a -> (e0 -> ExceptionalT e1 m a) -> ExceptionalT e1 m aSource
bracketT :: Monad m => ExceptionalT e m h -> (h -> ExceptionalT e m ()) -> (h -> ExceptionalT e m a) -> ExceptionalT e m aSource
If the enclosed monad has custom exception facilities, they could skip the cleanup code. Make sure, that this cannot happen by choosing an appropriate monad.
resolveT :: Monad m => (e -> m a) -> ExceptionalT e m a -> m aSource
tryT :: Monad m => ExceptionalT e m a -> m (Exceptional e a)Source
manyTSource
:: Monad m
=> e0 -> Maybe e1exception handler
-> a -> b -> bcons function
-> b
empty
-> ExceptionalT e0 m aatomic action to repeat
-> ExceptionalT e1 m b
Repeat an action until an exception occurs. Initialize the result with empty and add new elements using cons (e.g. [] and (:)). The exception handler decides whether the terminating exception is re-raised (Just) or catched (Nothing).
manyMonoidTSource
:: (Monad m, Monoid a)
=> e0 -> Maybe e1exception handler
-> ExceptionalT e0 m aatomic action to repeat
-> ExceptionalT e1 m a
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