Data.Acquire.Internal

Documentation

newtype Acquire a

A method for acquiring a scarce resource, providing the means of freeing it when no longer needed. This data type provides Functor/Applicative/Monad instances for composing different resources together. You can allocate these resources using either the bracket pattern (via with) or using ResourceT (via allocateAcquire).

This concept was originally introduced by Gabriel Gonzalez and described at: http://www.haskellforall.com/2013/06/the-resource-applicative.html. The implementation in this package is slightly different, due to taking a different approach to async exception safety.

Since: 1.1.0

Constructors

Acquire ((forall b. IO b -> IO b) -> IO (Allocated a))

Instances

MonadIO Acquire

Defined in Data.Acquire.Internal

Methods

liftIO :: IO a -> Acquire a

Applicative Acquire

Defined in Data.Acquire.Internal

Methods

pure :: a -> Acquire a

(<*>) :: Acquire (a -> b) -> Acquire a -> Acquire b

liftA2 :: (a -> b -> c) -> Acquire a -> Acquire b -> Acquire c

(*>) :: Acquire a -> Acquire b -> Acquire b

(<*) :: Acquire a -> Acquire b -> Acquire a

Functor Acquire

Defined in Data.Acquire.Internal

Methods

fmap :: (a -> b) -> Acquire a -> Acquire b

(<$) :: a -> Acquire b -> Acquire a

Monad Acquire

Defined in Data.Acquire.Internal

Methods

(>>=) :: Acquire a -> (a -> Acquire b) -> Acquire b

(>>) :: Acquire a -> Acquire b -> Acquire b

return :: a -> Acquire a

data Allocated a

Constructors

Allocated !a !(ReleaseType -> IO ())

with :: MonadUnliftIO m => Acquire a -> (a -> m b) -> m b

Allocate the given resource and provide it to the provided function. The resource will be freed as soon as the inner block is exited, whether normally or via an exception. This function is similar in function to bracket.

Since: 1.1.0

mkAcquire

Arguments

:: IO a

acquire the resource

-> (a -> IO ())

free the resource

-> Acquire a

Create an Acquire value using the given allocate and free functions.

To acquire and free the resource in an arbitrary monad with MonadUnliftIO, do the following:

acquire <- withRunInIO $ \runInIO ->
  return $ mkAcquire (runInIO create) (runInIO . free)

Note that this is only safe if the Acquire is run and freed within the same monadic scope it was created in.

Since: 1.1.0

data ReleaseType

The way in which a release is called.

Since: 1.1.2

Constructors

ReleaseEarly

ReleaseNormal

ReleaseExceptionWith SomeException

Bundled Patterns

pattern ReleaseException :: ReleaseType

Deprecated: Use ReleaseExceptionWith, which has the exception in the constructor. This pattern synonym hides the exception and can obscure problems.

Instances

Show ReleaseType

Defined in Data.Acquire.Internal

Methods

showsPrec :: Int -> ReleaseType -> ShowS

show :: ReleaseType -> String

showList :: [ReleaseType] -> ShowS

mkAcquireType

Arguments

:: IO a

acquire the resource

-> (a -> ReleaseType -> IO ())

free the resource

-> Acquire a

Same as mkAcquire, but the cleanup function will be informed of how cleanup was initiated. This allows you to distinguish, for example, between normal and exceptional exits.

To acquire and free the resource in an arbitrary monad with MonadUnliftIO, do the following:

acquire <- withRunInIO $ \runInIO ->
  return $ mkAcquireType (runInIO create) (\a -> runInIO . free a)

Note that this is only safe if the Acquire is run and freed within the same monadic scope it was created in.

Since: 1.1.2