Control.Lens.Internal.Exception

This module uses dirty tricks to generate a Handler from an arbitrary Fold.

Documentation

class Handleable e (m :: Type -> Type) (h :: Type -> Type) | h -> e m where

Both exceptions and Control.Exception provide a Handler type.

This lets us write combinators to build handlers that are agnostic about the choice of which of these they use.

Minimal complete definition

handler

Methods

handler :: Typeable a => Getting (First a) e a -> (a -> m r) -> h r

This builds a Handler for just the targets of a given Prism (or any Getter, really).

catches ... [ handler _AssertionFailed (s -> print $ "Assertion Failed\n" ++ s)
            , handler _ErrorCall (s -> print $ "Error\n" ++ s)
            ]

This works ith both the Handler type provided by Control.Exception:

handler :: Getter     SomeException a -> (a -> IO r) -> Handler r
handler :: Fold       SomeException a -> (a -> IO r) -> Handler r
handler :: Prism'     SomeException a -> (a -> IO r) -> Handler r
handler :: Lens'      SomeException a -> (a -> IO r) -> Handler r
handler :: Traversal' SomeException a -> (a -> IO r) -> Handler r

and with the Handler type provided by Control.Monad.Catch:

handler :: Getter     SomeException a -> (a -> m r) -> Handler m r
handler :: Fold       SomeException a -> (a -> m r) -> Handler m r
handler :: Prism'     SomeException a -> (a -> m r) -> Handler m r
handler :: Lens'      SomeException a -> (a -> m r) -> Handler m r
handler :: Traversal' SomeException a -> (a -> m r) -> Handler m r

and with the Handler type provided by Control.Monad.Error.Lens:

handler :: Getter     e a -> (a -> m r) -> Handler e m r
handler :: Fold       e a -> (a -> m r) -> Handler e m r
handler :: Prism'     e a -> (a -> m r) -> Handler e m r
handler :: Lens'      e a -> (a -> m r) -> Handler e m r
handler :: Traversal' e a -> (a -> m r) -> Handler e m r

handler_ :: Typeable a => Getting (First a) e a -> m r -> h r

This builds a Handler for just the targets of a given Prism (or any Getter, really). that ignores its input and just recovers with the stated monadic action.

catches ... [ handler_ _NonTermination (return "looped")
            , handler_ _StackOverflow (return "overflow")
            ]

This works with the Handler type provided by Control.Exception:

handler_ :: Getter     SomeException a -> IO r -> Handler r
handler_ :: Fold       SomeException a -> IO r -> Handler r
handler_ :: Prism'     SomeException a -> IO r -> Handler r
handler_ :: Lens'      SomeException a -> IO r -> Handler r
handler_ :: Traversal' SomeException a -> IO r -> Handler r

and with the Handler type provided by Control.Monad.Catch:

handler_ :: Getter     SomeException a -> m r -> Handler m r
handler_ :: Fold       SomeException a -> m r -> Handler m r
handler_ :: Prism'     SomeException a -> m r -> Handler m r
handler_ :: Lens'      SomeException a -> m r -> Handler m r
handler_ :: Traversal' SomeException a -> m r -> Handler m r

and with the Handler type provided by Control.Monad.Error.Lens:

handler_ :: Getter     e a -> m r -> Handler e m r
handler_ :: Fold       e a -> m r -> Handler e m r
handler_ :: Prism'     e a -> m r -> Handler e m r
handler_ :: Lens'      e a -> m r -> Handler e m r
handler_ :: Traversal' e a -> m r -> Handler e m r

Instances

Handleable SomeException IO Handler

Defined in Control.Lens.Internal.Exception

Methods

handler :: Typeable a => Getting (First a) SomeException a -> (a -> IO r) -> Handler r

handler_ :: Typeable a => Getting (First a) SomeException a -> IO r -> Handler r

Typeable m => Handleable SomeException m (Handler m)

Defined in Control.Lens.Internal.Exception

Methods

handler :: Typeable a => Getting (First a) SomeException a -> (a -> m r) -> Handler m r

handler_ :: Typeable a => Getting (First a) SomeException a -> m r -> Handler m r

Handleable e m (Handler e m)

Defined in Control.Monad.Error.Lens

Methods

handler :: Typeable a => Getting (First a) e a -> (a -> m r) -> Handler e m r

handler_ :: Typeable a => Getting (First a) e a -> m r -> Handler e m r

data HandlingException

There was an Exception caused by abusing the internals of a Handler.

Constructors

HandlingException

Instances

Show HandlingException

Defined in Control.Lens.Internal.Exception

Methods

showsPrec :: Int -> HandlingException -> ShowS

show :: HandlingException -> String

showList :: [HandlingException] -> ShowS

Exception HandlingException

Defined in Control.Lens.Internal.Exception

Methods

toException :: HandlingException -> SomeException

fromException :: SomeException -> Maybe HandlingException

displayException :: HandlingException -> String

AsHandlingException HandlingException

Defined in Control.Exception.Lens

Methods

__HandlingException :: Prism' HandlingException HandlingException

_HandlingException :: Prism' HandlingException ()