lens-3.9.2: Lenses, Folds and Traversals

Portabilitynon-portable
Stabilityexperimental
MaintainerEdward Kmett <ekmett@gmail.com>
Safe HaskellTrustworthy

Control.Lens.Internal.Exception

Description

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

Synopsis

Documentation

class Handleable e m h | h -> e m whereSource

Both MonadCatchIO-transformers 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.

Methods

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

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.CatchIO: 

 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_ :: Getting (First a) e a -> m r -> h rSource

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.CatchIO: 

 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

data HandlingException Source

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

Constructors

HandlingException 

Instances