Effectful.Internal.Env

The environment

data Env (es :: [Effect])

A strict (WHNF), thread local, mutable, extensible record indexed by types of kind Effect.

Supports forking, i.e. introduction of local branches for encapsulation of effects specific to effect handlers.

Warning: the environment is a mutable data structure and cannot be simultaneously used from multiple threads under any circumstances.

In order to pass it to a different thread, you need to perform a deep copy with the cloneEnv funtion.

Offers very good performance characteristics for most often performed operations:

• Extending: O(1) (amortized).
• Shrinking: O(1).
• Indexing via (:>): O(1)
• Modification of a specific element: O(1).
• Forking: O(n), where n is the size of the effect stack.
• Cloning: O(N + Σ(n_i)), where N is the size of the Storage, while i ranges over handlers of dynamically dispatched effects in the Storage and n_i is the size of the effect stack of i-th handler.

Constructors

Env

Fields

• envSize :: !Int
• envRefs :: !(IORef References)
• envStorage :: !(IORef Storage)

data References

An array of references to effects in the Storage.

Constructors

References

Fields

• refSize :: !Int
• refIndices :: !(MutablePrimArray RealWorld Int)

data Storage

A storage of effects.

Shared between all forks of the environment within the same thread.

Constructors

Storage

Fields

• stSize :: !Int
• stEffects :: !(SmallMutableArray RealWorld Any)
• stRelinkers :: !(SmallMutableArray RealWorld Any)

Relinker

newtype Relinker :: (Effect -> Type) -> Effect -> Type where

A function for relinking Env objects stored in the handlers and/or making a deep copy of the representation of the effect when cloning the environment.

Constructors

Relinker :: ((forall es. Env es -> IO (Env es)) -> rep e -> IO (rep e)) -> Relinker rep e

dummyRelinker :: Relinker rep e

A dummy Relinker.

Dispatch

data Dispatch

A type of dispatch. For more information consult the documentation in Effectful.Dispatch.Dynamic and Effectful.Dispatch.Static.

Constructors

Dynamic

Static SideEffects

data SideEffects

Signifies whether core operations of a statically dispatched effect perform side effects. If an effect is marked as such, the runStaticRep family of functions will require the IOE effect to be in context via the MaybeIOE type family.

Constructors

NoSideEffects

WithSideEffects

type family DispatchOf (e :: Effect) :: Dispatch

Dispatch types of effects.

Instances

type DispatchOf Prim

Defined in Effectful.Internal.Monad

type DispatchOf Prim = 'Static 'WithSideEffects

type DispatchOf IOE

Defined in Effectful.Internal.Monad

type DispatchOf IOE = 'Static 'WithSideEffects

type DispatchOf Fail

Defined in Effectful.Internal.Monad

type DispatchOf Fail = 'Dynamic

type DispatchOf (Error e)

Defined in Effectful.Error.Static

type DispatchOf (Error e) = 'Static 'NoSideEffects

type DispatchOf (Error e)

Defined in Effectful.Error.Dynamic

type DispatchOf (Error e) = 'Dynamic

type DispatchOf (Reader r)

Defined in Effectful.Reader.Static

type DispatchOf (Reader r) = 'Static 'NoSideEffects

type DispatchOf (Reader r)

Defined in Effectful.Reader.Dynamic

type DispatchOf (Reader r) = 'Dynamic

type DispatchOf (State s)

Defined in Effectful.State.Static.Local

type DispatchOf (State s) = 'Static 'NoSideEffects

type DispatchOf (State s)

Defined in Effectful.State.Static.Shared

type DispatchOf (State s) = 'Static 'NoSideEffects

type DispatchOf (State s)

Defined in Effectful.State.Dynamic

type DispatchOf (State s) = 'Dynamic

type DispatchOf (Writer w)

Defined in Effectful.Writer.Static.Local

type DispatchOf (Writer w) = 'Static 'NoSideEffects

type DispatchOf (Writer w)

Defined in Effectful.Writer.Static.Shared

type DispatchOf (Writer w) = 'Static 'NoSideEffects

type DispatchOf (Writer w)

Defined in Effectful.Writer.Dynamic

type DispatchOf (Writer w) = 'Dynamic

type family EffectRep (d :: Dispatch) :: Effect -> Type

Internal representations of effects.

Instances

type EffectRep 'Dynamic

Defined in Effectful.Internal.Monad

type EffectRep 'Dynamic = Handler

type EffectRep ('Static sideEffects)

Defined in Effectful.Internal.Monad

type EffectRep ('Static sideEffects) = StaticRep

Operations

emptyEnv :: IO (Env '[])

Create an empty environment.

cloneEnv :: Env es -> IO (Env es)

Clone the environment to use it in a different thread.

forkEnv :: Env es -> IO (Env es)

Create a fork of the environment.

Forked environment can be updated independently of the original one within the same thread.

sizeEnv :: Env es -> IO Int

Get the current size of the environment.

checkSizeEnv :: Env es -> IO ()

Check that the size of the environment is internally consistent.

tailEnv :: Env (e ': es) -> IO (Env es)

Access the tail of the environment.

Modification of the effect stack

consEnv

Arguments

:: EffectRep (DispatchOf e) e

The representation of the effect.

-> Relinker (EffectRep (DispatchOf e)) e

-> Env es

-> IO (Env (e ': es))

Extend the environment with a new data type (in place).

unconsEnv :: Env (e ': es) -> IO ()

Shrink the environment by one data type (in place).

Note: after calling this function the input environment is no longer usable.

replaceEnv

Arguments

:: forall e es. e :> es

=> EffectRep (DispatchOf e) e

The representation of the effect.

-> Relinker (EffectRep (DispatchOf e)) e

-> Env es

-> IO (Env es)

Replace a specific effect in the stack with a new value.

unreplaceEnv :: forall e es. e :> es => Env es -> IO ()

Remove a reference to the replaced effect.

Note: after calling this function the input environment is no longer usable.

subsumeEnv :: forall e es. e :> es => Env es -> IO (Env (e ': es))

Reference an existing effect from the top of the stack (in place).

unsubsumeEnv :: e :> es => Env (e ': es) -> IO ()

Remove a reference to an existing effect from the top of the stack.

Note: after calling this function the input environment is no longer usable.

injectEnv :: forall xs es. Subset xs es => Env es -> IO (Env xs)

Construct an environment containing a permutation (with possible duplicates) of a subset of effects from the input environment.

Data retrieval and update

getEnv

Arguments

:: forall e es. e :> es

=> Env es

The environment.

-> IO (EffectRep (DispatchOf e) e)

Extract a specific data type from the environment.

putEnv

Arguments

:: forall e es. e :> es

=> Env es

The environment.

-> EffectRep (DispatchOf e) e

-> IO ()

Replace the data type in the environment with a new value (in place).

stateEnv

Arguments

:: forall e es a. e :> es

=> Env es

The environment.

-> (EffectRep (DispatchOf e) e -> (a, EffectRep (DispatchOf e) e))

-> IO a

Modify the data type in the environment (in place) and return a value.

modifyEnv

Arguments

:: forall e es. e :> es

=> Env es

The environment.

-> (EffectRep (DispatchOf e) e -> EffectRep (DispatchOf e) e)

-> IO ()

Modify the data type in the environment (in place).