Copyright	(C) 2013-2016 Edward Kmett
License	BSD-style (see the file LICENSE)
Maintainer	Edward Kmett <ekmett@gmail.com>
Stability	experimental
Portability	non-portable
Safe Haskell	Safe-Inferred
Language	Haskell2010

Control.Lens.Internal.Exception

Description

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

Synopsis

class Handleable e (m :: * -> *) (h :: * -> *) | h -> e m where
- handler :: Typeable a => Getting (First a) e a -> (a -> m r) -> h r
- handler_ :: Typeable a => Getting (First a) e a -> m r -> h r
data HandlingException = HandlingException

Documentation

class Handleable e (m :: * -> *) (h :: * -> *) | 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

Instances details

Handleable SomeException IO Handler #
Instance details 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) #
Instance details 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) #
Instance details 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

Instances details

Show HandlingException #
Instance details Defined in Control.Lens.Internal.Exception Methods showsPrec :: Int -> HandlingException -> ShowS # show :: HandlingException -> String # showList :: [HandlingException] -> ShowS #
Exception HandlingException #
Instance details Defined in Control.Lens.Internal.Exception Methods toException :: HandlingException -> SomeException # fromException :: SomeException -> Maybe HandlingException # displayException :: HandlingException -> String #
AsHandlingException HandlingException #
Instance details Defined in Control.Exception.Lens Methods __HandlingException :: Prism' HandlingException HandlingException # _HandlingException :: Prism' HandlingException () #