Safe Haskell	None
Language	Haskell2010

Control.Effect.Reader

Contents

Reader effect
Re-exports

Description

An effect providing access to an immutable (but locally-modifiable) context value.

This effect is similar to the traditional MonadReader typeclass, though it allows the presence of multiple Reader t effects.

Predefined carriers:

Control.Carrier.Reader.
Control.Monad.Trans.Reader.
Control.Monad.Trans.RWS.Lazy
Control.Monad.Trans.RWS.Strict
If Reader r is the last effect in a stack, it can be interpreted directly to (-> r) (a function taking an r).

Since: 0.1.0.0

Synopsis

data Reader r m k
- = Ask (r -> m k)
- | forall b. Local (r -> r) (m b) (b -> m k)
ask :: Has (Reader r) sig m => m r
asks :: Has (Reader r) sig m => (r -> a) -> m a
local :: Has (Reader r) sig m => (r -> r) -> m a -> m a
class (HFunctor sig, Monad m) => Algebra sig m | m -> sig
class HFunctor sig => Effect sig
type Has eff sig m = (Members eff sig, Algebra sig m)
run :: Identity a -> a

Reader effect

data Reader r m k Source #

Since: 0.1.0.0

Constructors

Ask (r -> m k)
forall b. Local (r -> r) (m b) (b -> m k)

Instances

Instances details

Effect (Reader r) Source #
Instance details Defined in Control.Effect.Reader.Internal Methods thread :: (Functor ctx, Monad m) => ctx () -> (forall x. ctx (m x) -> n (ctx x)) -> Reader r m a -> Reader r n (ctx a) Source #
HFunctor (Reader r) Source #
Instance details Defined in Control.Effect.Reader.Internal Methods hmap :: Functor m => (forall x. m x -> n x) -> Reader r m a -> Reader r n a Source #
Algebra (Reader r) ((->) r :: Type -> Type) Source #
Instance details Defined in Control.Algebra Methods alg :: Reader r ((->) r) a -> r -> a Source #
Functor m => Functor (Reader r m) Source #
Instance details Defined in Control.Effect.Reader.Internal Methods fmap :: (a -> b) -> Reader r m a -> Reader r m b # (<$) :: a -> Reader r m b -> Reader r m a #
Algebra sig m => Algebra (Reader r :+: sig) (ReaderT r m) Source #
Instance details Defined in Control.Algebra Methods alg :: (Reader r :+: sig) (ReaderT r m) a -> ReaderT r m a Source #
Algebra sig m => Algebra (Reader r :+: sig) (ReaderC r m) Source #
Instance details Defined in Control.Carrier.Reader Methods alg :: (Reader r :+: sig) (ReaderC r m) a -> ReaderC r m a Source #
(Algebra sig m, Effect sig, Monoid w) => Algebra (Reader r :+: (Writer w :+: (State s :+: sig))) (RWST r w s m) Source #
Instance details Defined in Control.Algebra Methods alg :: (Reader r :+: (Writer w :+: (State s :+: sig))) (RWST r w s m) a -> RWST r w s m a Source #
(Algebra sig m, Effect sig, Monoid w) => Algebra (Reader r :+: (Writer w :+: (State s :+: sig))) (RWST r w s m) Source #
Instance details Defined in Control.Algebra Methods alg :: (Reader r :+: (Writer w :+: (State s :+: sig))) (RWST r w s m) a -> RWST r w s m a Source #

ask :: Has (Reader r) sig m => m r Source #

Retrieve the environment value.

runReader a (ask >>= k) = runReader a (k a)

Since: 0.1.0.0

asks :: Has (Reader r) sig m => (r -> a) -> m a Source #

Project a function out of the current environment value.

asks f = fmap f ask

Since: 0.1.0.0

local :: Has (Reader r) sig m => (r -> r) -> m a -> m a Source #

Run a computation with an environment value locally modified by the passed function.

runReader a (local f m) = runReader (f a) m

Since: 0.1.0.0

Re-exports

class (HFunctor sig, Monad m) => Algebra sig m | m -> sig Source #

The class of carriers (results) for algebras (effect handlers) over signatures (effects), whose actions are given by the alg method.

Since: 1.0.0.0

Minimal complete definition

alg

Instances

Instances details

Algebra Choose NonEmpty Source #
Instance details Defined in Control.Algebra Methods alg :: Choose NonEmpty a -> NonEmpty a Source #
Algebra Empty Maybe Source #
Instance details Defined in Control.Algebra Methods alg :: Empty Maybe a -> Maybe a Source #
Algebra NonDet [] Source #
Instance details Defined in Control.Algebra Methods alg :: NonDet [] a -> [a] Source #
Algebra sig m => Algebra sig (Alt m) Source #	This instance permits effectful actions to be lifted into the `Alt` monad, which eases the invocation of repeated alternation with `<\|>`: a <\|> b <\|> c <\|> d is equivalent to getAlt (mconcat [a, b, c, d]) Since: 1.0.1.0
Instance details Defined in Control.Algebra Methods alg :: sig (Alt m) a -> Alt m a Source #
Algebra sig m => Algebra sig (Ap m) Source #	This instance permits effectful actions to be lifted into the `Ap` monad given a monoidal return type, which can provide clarity when chaining calls to `mappend`. mappend <$> act1 <> (mappend <$> act2 <> act3) is equivalent to getAp (act1 <> act2 <> act3) Since: 1.0.1.0
Instance details Defined in Control.Algebra Methods alg :: sig (Ap m) a -> Ap m a Source #
Algebra sig m => Algebra sig (IdentityT m) Source #
Instance details Defined in Control.Algebra Methods alg :: sig (IdentityT m) a -> IdentityT m a Source #
Algebra (Lift IO) IO Source #
Instance details Defined in Control.Algebra Methods alg :: Lift IO IO a -> IO a Source #
Algebra (Lift Identity) Identity Source #
Instance details Defined in Control.Algebra Methods alg :: Lift Identity Identity a -> Identity a Source #
Monad m => Algebra (Lift m) (LiftC m) Source #
Instance details Defined in Control.Carrier.Lift Methods alg :: Lift m (LiftC m) a -> LiftC m a Source #
Algebra (Error e) (Either e) Source #
Instance details Defined in Control.Algebra Methods alg :: Error e (Either e) a -> Either e a Source #
Monoid w => Algebra (Writer w) ((,) w) Source #
Instance details Defined in Control.Algebra Methods alg :: Writer w ((,) w) a -> (w, a) Source #
Algebra (Reader r) ((->) r :: Type -> Type) Source #
Instance details Defined in Control.Algebra Methods alg :: Reader r ((->) r) a -> r -> a Source #
(Algebra sig m, Effect sig) => Algebra (Choose :+: sig) (ChooseC m) Source #
Instance details Defined in Control.Carrier.Choose.Church Methods alg :: (Choose :+: sig) (ChooseC m) a -> ChooseC m a Source #
(Algebra sig m, Effect sig) => Algebra (Empty :+: sig) (EmptyC m) Source #
Instance details Defined in Control.Carrier.Empty.Maybe Methods alg :: (Empty :+: sig) (EmptyC m) a -> EmptyC m a Source #
(Algebra sig m, Effect sig) => Algebra (NonDet :+: sig) (NonDetC m) Source #
Instance details Defined in Control.Carrier.NonDet.Church Methods alg :: (NonDet :+: sig) (NonDetC m) a -> NonDetC m a Source #
(MonadIO m, Algebra sig m) => Algebra (Trace :+: sig) (TraceC m) Source #
Instance details Defined in Control.Carrier.Trace.Printing Methods alg :: (Trace :+: sig) (TraceC m) a -> TraceC m a Source #
Algebra sig m => Algebra (Trace :+: sig) (TraceC m) Source #
Instance details Defined in Control.Carrier.Trace.Ignoring Methods alg :: (Trace :+: sig) (TraceC m) a -> TraceC m a Source #
(Algebra sig m, Effect sig) => Algebra (Trace :+: sig) (TraceC m) Source #
Instance details Defined in Control.Carrier.Trace.Returning Methods alg :: (Trace :+: sig) (TraceC m) a -> TraceC m a Source #
(Algebra sig m, Effect sig) => Algebra (Fail :+: sig) (FailC m) Source #
Instance details Defined in Control.Carrier.Fail.Either Methods alg :: (Fail :+: sig) (FailC m) a -> FailC m a Source #
(Algebra sig m, Effect sig) => Algebra (Fresh :+: sig) (FreshC m) Source #
Instance details Defined in Control.Carrier.Fresh.Strict Methods alg :: (Fresh :+: sig) (FreshC m) a -> FreshC m a Source #
(Algebra sig m, Effect sig) => Algebra (Cut :+: (NonDet :+: sig)) (CutC m) Source #
Instance details Defined in Control.Carrier.Cut.Church Methods alg :: (Cut :+: (NonDet :+: sig)) (CutC m) a -> CutC m a Source #
(Algebra sig m, Effect sig) => Algebra (Cull :+: (NonDet :+: sig)) (CullC m) Source #
Instance details Defined in Control.Carrier.Cull.Church Methods alg :: (Cull :+: (NonDet :+: sig)) (CullC m) a -> CullC m a Source #
Algebra sig m => Algebra (Reader r :+: sig) (ReaderT r m) Source #
Instance details Defined in Control.Algebra Methods alg :: (Reader r :+: sig) (ReaderT r m) a -> ReaderT r m a Source #
Algebra sig m => Algebra (Reader r :+: sig) (ReaderC r m) Source #
Instance details Defined in Control.Carrier.Reader Methods alg :: (Reader r :+: sig) (ReaderC r m) a -> ReaderC r m a Source #
(Algebra sig m, Effect sig) => Algebra (State s :+: sig) (StateT s m) Source #
Instance details Defined in Control.Algebra Methods alg :: (State s :+: sig) (StateT s m) a -> StateT s m a Source #
(Algebra sig m, Effect sig) => Algebra (State s :+: sig) (StateT s m) Source #
Instance details Defined in Control.Algebra Methods alg :: (State s :+: sig) (StateT s m) a -> StateT s m a Source #
(Algebra sig m, Effect sig) => Algebra (State s :+: sig) (StateC s m) Source #
Instance details Defined in Control.Carrier.State.Strict Methods alg :: (State s :+: sig) (StateC s m) a -> StateC s m a Source #
(Algebra sig m, Effect sig) => Algebra (State s :+: sig) (StateC s m) Source #
Instance details Defined in Control.Carrier.State.Lazy Methods alg :: (State s :+: sig) (StateC s m) a -> StateC s m a Source #
(Algebra sig m, Effect sig) => Algebra (Throw e :+: sig) (ThrowC e m) Source #
Instance details Defined in Control.Carrier.Throw.Either Methods alg :: (Throw e :+: sig) (ThrowC e m) a -> ThrowC e m a Source #
(Algebra sig m, Effect sig) => Algebra (Error e :+: sig) (ExceptT e m) Source #
Instance details Defined in Control.Algebra Methods alg :: (Error e :+: sig) (ExceptT e m) a -> ExceptT e m a Source #
(Algebra sig m, Effect sig) => Algebra (Error e :+: sig) (ErrorC e m) Source #
Instance details Defined in Control.Carrier.Error.Either Methods alg :: (Error e :+: sig) (ErrorC e m) a -> ErrorC e m a Source #
(Algebra sig m, Effect sig, Monoid w) => Algebra (Writer w :+: sig) (WriterT w m) Source #
Instance details Defined in Control.Algebra Methods alg :: (Writer w :+: sig) (WriterT w m) a -> WriterT w m a Source #
(Algebra sig m, Effect sig, Monoid w) => Algebra (Writer w :+: sig) (WriterT w m) Source #
Instance details Defined in Control.Algebra Methods alg :: (Writer w :+: sig) (WriterT w m) a -> WriterT w m a Source #
(Monoid w, Algebra sig m, Effect sig) => Algebra (Writer w :+: sig) (WriterC w m) Source #
Instance details Defined in Control.Carrier.Writer.Strict Methods alg :: (Writer w :+: sig) (WriterC w m) a -> WriterC w m a Source #
(HFunctor eff, HFunctor sig, Reifies s (Handler eff m), Monad m, Algebra sig m) => Algebra (eff :+: sig) (InterpretC s eff m) Source #
Instance details Defined in Control.Carrier.Interpret Methods alg :: (eff :+: sig) (InterpretC s eff m) a -> InterpretC s eff m a Source #
(Algebra sig m, Effect sig, Monoid w) => Algebra (Reader r :+: (Writer w :+: (State s :+: sig))) (RWST r w s m) Source #
Instance details Defined in Control.Algebra Methods alg :: (Reader r :+: (Writer w :+: (State s :+: sig))) (RWST r w s m) a -> RWST r w s m a Source #
(Algebra sig m, Effect sig, Monoid w) => Algebra (Reader r :+: (Writer w :+: (State s :+: sig))) (RWST r w s m) Source #
Instance details Defined in Control.Algebra Methods alg :: (Reader r :+: (Writer w :+: (State s :+: sig))) (RWST r w s m) a -> RWST r w s m a Source #

class HFunctor sig => Effect sig Source #

The class of effect types, which must:

Be functorial in their last two arguments, and
Support threading effects in higher-order positions through using the carrier’s suspended context.

All first-order effects (those without existential occurrences of m) admit a default definition of thread provided a Generic1 instance is available for the effect.

Since: 1.0.0.0

Instances

Instances details

Effect Choose Source #
Instance details Defined in Control.Effect.Choose.Internal Methods thread :: (Functor ctx, Monad m) => ctx () -> (forall x. ctx (m x) -> n (ctx x)) -> Choose m a -> Choose n (ctx a) Source #
Effect Empty Source #
Instance details Defined in Control.Effect.Empty.Internal Methods thread :: (Functor ctx, Monad m) => ctx () -> (forall x. ctx (m x) -> n (ctx x)) -> Empty m a -> Empty n (ctx a) Source #
Effect Trace Source #
Instance details Defined in Control.Effect.Trace Methods thread :: (Functor ctx, Monad m) => ctx () -> (forall x. ctx (m x) -> n (ctx x)) -> Trace m a -> Trace n (ctx a) Source #
Effect Fresh Source #
Instance details Defined in Control.Effect.Fresh Methods thread :: (Functor ctx, Monad m) => ctx () -> (forall x. ctx (m x) -> n (ctx x)) -> Fresh m a -> Fresh n (ctx a) Source #
Effect Cut Source #
Instance details Defined in Control.Effect.Cut Methods thread :: (Functor ctx, Monad m) => ctx () -> (forall x. ctx (m x) -> n (ctx x)) -> Cut m a -> Cut n (ctx a) Source #
Effect Cull Source #
Instance details Defined in Control.Effect.Cull Methods thread :: (Functor ctx, Monad m) => ctx () -> (forall x. ctx (m x) -> n (ctx x)) -> Cull m a -> Cull n (ctx a) Source #
Effect (Catch e) Source #
Instance details Defined in Control.Effect.Catch.Internal Methods thread :: (Functor ctx, Monad m) => ctx () -> (forall x. ctx (m x) -> n (ctx x)) -> Catch e m a -> Catch e n (ctx a) Source #
Functor sig => Effect (Lift sig) Source #
Instance details Defined in Control.Effect.Lift.Internal Methods thread :: (Functor ctx, Monad m) => ctx () -> (forall x. ctx (m x) -> n (ctx x)) -> Lift sig m a -> Lift sig n (ctx a) Source #
Effect (Reader r) Source #
Instance details Defined in Control.Effect.Reader.Internal Methods thread :: (Functor ctx, Monad m) => ctx () -> (forall x. ctx (m x) -> n (ctx x)) -> Reader r m a -> Reader r n (ctx a) Source #
Effect (State s) Source #
Instance details Defined in Control.Effect.State.Internal Methods thread :: (Functor ctx, Monad m) => ctx () -> (forall x. ctx (m x) -> n (ctx x)) -> State s m a -> State s n (ctx a) Source #
Effect (Throw e) Source #
Instance details Defined in Control.Effect.Throw.Internal Methods thread :: (Functor ctx, Monad m) => ctx () -> (forall x. ctx (m x) -> n (ctx x)) -> Throw e m a -> Throw e n (ctx a) Source #
Effect (Writer w) Source #
Instance details Defined in Control.Effect.Writer.Internal Methods thread :: (Functor ctx, Monad m) => ctx () -> (forall x. ctx (m x) -> n (ctx x)) -> Writer w m a -> Writer w n (ctx a) Source #
(Effect f, Effect g) => Effect (f :+: g) Source #
Instance details Defined in Control.Effect.Sum Methods thread :: (Functor ctx, Monad m) => ctx () -> (forall x. ctx (m x) -> n (ctx x)) -> (f :+: g) m a -> (f :+: g) n (ctx a) Source #

type Has eff sig m = (Members eff sig, Algebra sig m) Source #

m is a carrier for sig containing eff.

Note that if eff is a sum, it will be decomposed into multiple Member constraints. While this technically allows one to combine multiple unrelated effects into a single Has constraint, doing so has two significant drawbacks:

Due to a problem with recursive type families, this can lead to significantly slower compiles.
It defeats ghc’s warnings for redundant constraints, and thus can lead to a proliferation of redundant constraints as code is changed.

run :: Identity a -> a Source #

Run an action exhausted of effects to produce its final result value.

Since: 1.0.0.0