Exception

ghc-7.10.3: The GHC API

Safe Haskell | Safe
Language | Haskell2010

Exception

Synopsis

- module Control.Exception
- catchIO :: IO a -> (IOException -> IO a) -> IO a
- handleIO :: (IOException -> IO a) -> IO a -> IO a
- tryIO :: IO a -> IO (Either IOException a)
- class MonadIO m => ExceptionMonad m where
  - gcatch :: Exception e => m a -> (e -> m a) -> m a
  - gmask :: ((m a -> m a) -> m b) -> m b
  - gbracket :: m a -> (a -> m b) -> (a -> m c) -> m c
  - gfinally :: m a -> m b -> m a
- gtry :: (ExceptionMonad m, Exception e) => m a -> m (Either e a)
- ghandle :: (ExceptionMonad m, Exception e) => (e -> m a) -> m a -> m a
- gonException :: ExceptionMonad m => m a -> m b -> m a

# Documentation

module Control.Exception

catchIO :: IO a -> (IOException -> IO a) -> IO a

handleIO :: (IOException -> IO a) -> IO a -> IO a

tryIO :: IO a -> IO (Either IOException a)

class MonadIO m => ExceptionMonad m where

A monad that can catch exceptions. A minimal definition requires a definition of `gcatch`.

Implementations on top of `IO` should implement `gmask` to eventually call the primitive `mask`. These are used for implementations that support asynchronous exceptions. The default implementations of `gbracket` and `gfinally` use `gmask` thus rarely require overriding.

Minimal complete definition

gcatch, gmask

Methods

gcatch :: Exception e => m a -> (e -> m a) -> m a

Generalised version of `catch`, allowing an arbitrary exception handling monad instead of just `IO`.

gmask :: ((m a -> m a) -> m b) -> m b

Generalised version of `mask_`, allowing an arbitrary exception handling monad instead of just `IO`.

gbracket :: m a -> (a -> m b) -> (a -> m c) -> m c

Generalised version of `bracket`, allowing an arbitrary exception handling monad instead of just `IO`.

gfinally :: m a -> m b -> m a

Generalised version of `finally`, allowing an arbitrary exception handling monad instead of just `IO`.

Instances

ExceptionMonad IO |
ExceptionMonad Ghc |
ExceptionMonad m => ExceptionMonad (GhcT m) |

gtry :: (ExceptionMonad m, Exception e) => m a -> m (Either e a)

ghandle :: (ExceptionMonad m, Exception e) => (e -> m a) -> m a -> m a

Generalised version of `handle`, allowing an arbitrary exception handling monad instead of just `IO`.

gonException :: ExceptionMonad m => m a -> m b -> m a

Always executes the first argument. If this throws an exception the second argument is executed and the exception is raised again.