Control.Monad.Error.Interface

The Error monad (also called the Exception monad).

Definitions

interface MonadError : Type -> (Type -> Type) -> Type

  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 `Either String` 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 'MonadError' class.

Parameters: e, m
Constraints: Monad m
Methods:

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:
  
  ```idris example
  do { action1; action2; action3 } `catchError` handler
  ```

Implementations:

MonadError () Maybe

Monad m => MonadError () (MaybeT m)

MonadError e (Either e)

Monad m => MonadError e (EitherT e m)

MonadError e m => MonadError e (MaybeT m)

MonadError e m => MonadError e (ReaderT r m)

MonadError e m => MonadError e (StateT r m)

MonadError e m => MonadError e (RWST r w s m)

MonadError e m => MonadError e (WriterT w m)

throwError : MonadError e m => e -> m a

  Is used within a monadic computation to begin exception processing.

Totality: total
Visibility: public export

catchError : MonadError e m => m a -> (e -> m a) -> m a

  A handler function to handle previous errors and return to normal execution.
  A common idiom is:
  
  ```idris example
  do { action1; action2; action3 } `catchError` handler
  ```

Totality: total
Visibility: public export

liftEither : MonadError e m => Either e a -> m a

  Lifts an `Either e` into any `MonadError e`.

Totality: total
Visibility: public export

tryError : MonadError e m => m a -> m (Either e a)

  Makes a success or failure of an action visible in
  the return type.

Totality: total
Visibility: public export

withError : MonadError e m => (e -> e) -> m a -> m a

  `MonadError` analogue to the `withEitherT` function.
  Modify the value (but not the type) of an error.
  If you need to change the type of `e` use `mapError`.

Totality: total
Visibility: public export

handleError : MonadError e m => (e -> m a) -> m a -> m a

  Flipped version of `catchError`.

Totality: total
Visibility: public export

mapError : (MonadError e m, MonadError e' n) => (m (Either e a) -> n (Either e' b)) -> m a -> n b

  `MonadError` analogue of the `mapEitherT` function.  The
  computation is unwrapped, a function is applied to the `Either`, and
  the result is lifted into the second `MonadError` instance.

Totality: total
Visibility: public export