Safe Haskell | Safe-Inferred |
---|---|
Language | Haskell98 |
Wrapper for Control.Monad.Except from the mtl package
- class Error a where
- type ExceptT = ErrorT
- mkExceptT :: m (Either e a) -> ExceptT e m a
- class Monad m => MonadError e m | m -> e where
- throwError :: e -> m a
- catchError :: m a -> (e -> m a) -> m a
- runExceptT :: ExceptT e m a -> m (Either e a)
Documentation
class Error a where
Nothing
Error () | To simulate |
Error IOException | |
Error DeclarationException | |
Error TCErr | |
Error TypeError | |
Error UnquoteError | |
Error SplitError | |
Error SplitError | |
Error InvertExcept | |
Error ProjVarExc | |
Error UnifyException | |
ErrorList a => Error [a] | A string can be thrown as an error. |
Error (a, b, c) |
mkExceptT :: m (Either e a) -> ExceptT e m a Source
We cannot define data constructors synonymous, so we define the
mkExceptT
function to be used instead of the data constructor
ErrorT
.
class Monad m => MonadError e m | m -> e where
The strategy of combining computations that can throw exceptions by bypassing bound functions from the point an exception is thrown to the point that it is handled.
Is parameterized over the type of error information and
the monad type constructor.
It is common to use
as the monad type constructor
for an error monad in which error descriptions take the form of strings.
In that case and many other common cases the resulting monad is already defined
as an instance of the Either
StringMonadError
class.
You can also define your own error type and/or use a monad type constructor
other than
or Either
String
.
In these cases you will have to explicitly define instances of the Either
IOError
Error
and/or MonadError
classes.
throwError :: e -> m a
Is used within a monadic computation to begin exception processing.
catchError :: m a -> (e -> m a) -> m a
A handler function to handle previous errors and return to normal execution. A common idiom is:
do { action1; action2; action3 } `catchError` handler
where the action
functions can call throwError
.
Note that handler
and the do-block must have the same return type.
MonadError IOException IO | |
MonadError ParseError Parser | |
MonadError TCErr IM | |
MonadError TCErr TerM | |
MonadError e m => MonadError e (MaybeT m) | |
MonadError e m => MonadError e (ListT m) | |
MonadError e m => MonadError e (IdentityT m) | |
MonadError e (Either e) | |
MonadError TCErr (TCMT IO) | |
(Monoid w, MonadError e m) => MonadError e (WriterT w m) | |
(Monoid w, MonadError e m) => MonadError e (WriterT w m) | |
MonadError e m => MonadError e (StateT s m) | |
MonadError e m => MonadError e (StateT s m) | |
MonadError e m => MonadError e (ReaderT r m) | |
(Monad m, Error e) => MonadError e (ErrorT e m) | |
MonadError e m => MonadError e (STT s m) | |
(Error err, MonadError err' m) => MonadError err' (ExceptionT err m) | |
(Monoid w, MonadError e m) => MonadError e (RWST r w s m) | |
(Monoid w, MonadError e m) => MonadError e (RWST r w s m) | |
MonadError e m => MonadError e (EquivT s c v m) |
runExceptT :: ExceptT e m a -> m (Either e a) Source
runExcept
function using mtl 2.1.*.