Polysemy.Resource

Effect

data Resource m a where

An effect capable of providing bracket semantics. Interpreters for this will successfully run the deallocation action even in the presence of other short-circuiting effects.

Constructors

Bracket :: m a -> (a -> m c) -> (a -> m b) -> Resource m b

BracketOnError :: m a -> (a -> m c) -> (a -> m b) -> Resource m b

Actions

bracket :: forall r a c b. Member Resource r => Sem r a -> (a -> Sem r c) -> (a -> Sem r b) -> Sem r b

bracket_

Arguments

:: Member Resource r

=> Sem r a

computation to run first

-> Sem r b

computation to run last (even if an exception was raised)

-> Sem r c

computation to run in-between

-> Sem r c

A variant of bracket where the return value from the first computation is not required.

cf. bracket and bracket_

Since: 1.5.0.0

bracketOnError :: forall r a c b. Member Resource r => Sem r a -> (a -> Sem r c) -> (a -> Sem r b) -> Sem r b

finally

Arguments

:: Member Resource r

=> Sem r a

computation to run first

-> Sem r b

computation to run afterward (even if an exception was raised)

-> Sem r a

Like bracket, but for the simple case of one computation to run afterward.

Since: 0.4.0.0

onException

Arguments

:: Member Resource r

=> Sem r a

computation to run first

-> Sem r b

computation to run afterward if an exception was raised

-> Sem r a

Like bracketOnError, but for the simple case of one computation to run afterward.

Since: 0.4.0.0

Interpretations

runResource :: forall r a. Sem (Resource ': r) a -> Sem r a

Run a Resource effect purely.

Since: 1.0.0.0

resourceToIOFinal :: Member (Final IO) r => Sem (Resource ': r) a -> Sem r a

Run a Resource effect in terms of bracket through final IO

Beware: Effects that aren't interpreted in terms of IO will have local state semantics in regards to Resource effects interpreted this way. See Final.

Notably, unlike resourceToIO, this is not consistent with State unless runStateInIORef is used. State that seems like it should be threaded globally throughout brackets will not be.

Use resourceToIO instead if you need to run pure, stateful interpreters after the interpreter for Resource. (Pure interpreters are interpreters that aren't expressed in terms of another effect or monad; for example, runState.)

Since: 1.2.0.0

resourceToIO :: forall r a. Member (Embed IO) r => Sem (Resource ': r) a -> Sem r a

A more flexible --- though less safe --- version of resourceToIOFinal

This function is capable of running Resource effects anywhere within an effect stack, without relying on an explicit function to lower it into IO. Notably, this means that State effects will be consistent in the presence of Resource.

ResourceToIO' is safe whenever you're concerned about exceptions thrown by effects _already handled_ in your effect stack, or in IO code run directly inside of bracket. It is not safe against exceptions thrown explicitly at the main thread. If this is not safe enough for your use-case, use resourceToIOFinal instead.

This function creates a thread, and so should be compiled with -threaded.

Since: 1.0.0.0

lowerResource

Arguments

:: forall r a. Member (Embed IO) r

=> (forall x. Sem r x -> IO x)

Strategy for lowering a Sem action down to IO. This is likely some combination of runM and other interpreters composed via .@.

-> Sem (Resource ': r) a

-> Sem r a

Deprecated: Use resourceToIOFinal instead

Run a Resource effect in terms of bracket.

Since: 1.0.0.0