Safe Haskell	Safe-Inferred
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 where
- Ask :: Reader r m r
- Local :: (r -> r) -> m a -> Reader r m a
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 Monad m => Algebra sig m | m -> sig
type Has eff sig m = (Members eff sig, Algebra sig m)
run :: Identity a -> a

Reader effect

data Reader r m k where Source #

Since: 0.1.0.0

Constructors

Ask :: Reader r m r
Local :: (r -> r) -> m a -> Reader r m a

Instances

Instances details

Algebra (Reader r) ((->) r) Source #
Instance details Defined in Control.Algebra Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n ((->) r) -> Reader r n a -> ctx () -> r -> ctx a Source #
Algebra sig m => Algebra (Reader r :+: sig) (ReaderC r m) Source #
Instance details Defined in Control.Carrier.Reader Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (ReaderC r m) -> (Reader r :+: sig) n a -> ctx () -> ReaderC r m (ctx a) Source #
Algebra sig m => Algebra (Reader r :+: sig) (ReaderT r m) Source #
Instance details Defined in Control.Algebra Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (ReaderT r m) -> (Reader r :+: sig) n a -> ctx () -> ReaderT r m (ctx a) Source #
(Algebra sig m, Monoid w) => Algebra (Reader r :+: (Writer w :+: (State s :+: sig))) (RWST r w s m) Source #
Instance details Defined in Control.Algebra Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (RWST r w s m) -> (Reader r :+: (Writer w :+: (State s :+: sig))) n a -> ctx () -> RWST r w s m (ctx a) Source #
(Algebra sig m, Monoid w) => Algebra (Reader r :+: (Writer w :+: (State s :+: sig))) (RWST r w s m) Source #
Instance details Defined in Control.Algebra Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (RWST r w s m) -> (Reader r :+: (Writer w :+: (State s :+: sig))) n a -> ctx () -> RWST r w s m (ctx a) Source #
(Algebra sig m, Monoid w) => Algebra (Reader r :+: (Writer w :+: (State s :+: sig))) (RWST r w s m) Source #
Instance details Defined in Control.Algebra Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (RWST r w s m) -> (Reader r :+: (Writer w :+: (State s :+: sig))) n a -> ctx () -> RWST r w s m (ctx 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 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 :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n NonEmpty -> Choose n a -> ctx () -> NonEmpty (ctx a) Source #
Algebra Empty Maybe Source #
Instance details Defined in Control.Algebra Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n Maybe -> Empty n a -> ctx () -> Maybe (ctx a) Source #
Algebra NonDet [] Source #
Instance details Defined in Control.Algebra Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n [] -> NonDet n a -> ctx () -> [ctx 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 :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (Ap m) -> sig n a -> ctx () -> Ap m (ctx 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 :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (Alt m) -> sig n a -> ctx () -> Alt m (ctx a) Source #
Algebra sig m => Algebra sig (IdentityT m) Source #
Instance details Defined in Control.Algebra Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (IdentityT m) -> sig n a -> ctx () -> IdentityT m (ctx a) Source #
Algebra (Lift Identity) Identity Source #
Instance details Defined in Control.Algebra Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n Identity -> Lift Identity n a -> ctx () -> Identity (ctx a) Source #
Algebra (Lift IO) IO Source #
Instance details Defined in Control.Algebra Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n IO -> Lift IO n a -> ctx () -> IO (ctx a) Source #
Algebra (Error e) (Either e) Source #
Instance details Defined in Control.Algebra Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (Either e) -> Error e n a -> ctx () -> Either e (ctx a) Source #
Monad m => Algebra (Lift m) (LiftC m) Source #
Instance details Defined in Control.Carrier.Lift Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (LiftC m) -> Lift m n a -> ctx () -> LiftC m (ctx a) Source #
Monoid w => Algebra (Writer w) ((,) w) Source #
Instance details Defined in Control.Algebra Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n ((,) w) -> Writer w n a -> ctx () -> (w, ctx a) Source #
Algebra (Reader r) ((->) r) Source #
Instance details Defined in Control.Algebra Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n ((->) r) -> Reader r n a -> ctx () -> r -> ctx a Source #
Algebra sig m => Algebra (Choose :+: sig) (ChooseC m) Source #
Instance details Defined in Control.Carrier.Choose.Church Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (ChooseC m) -> (Choose :+: sig) n a -> ctx () -> ChooseC m (ctx a) Source #
Algebra sig m => Algebra (Cull :+: (NonDet :+: sig)) (CullC m) Source #
Instance details Defined in Control.Carrier.Cull.Church Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (CullC m) -> (Cull :+: (NonDet :+: sig)) n a -> ctx () -> CullC m (ctx a) Source #
Algebra sig m => Algebra (Cut :+: (NonDet :+: sig)) (CutC m) Source #
Instance details Defined in Control.Carrier.Cut.Church Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (CutC m) -> (Cut :+: (NonDet :+: sig)) n a -> ctx () -> CutC m (ctx a) Source #
Algebra sig m => Algebra (Empty :+: sig) (EmptyC m) Source #
Instance details Defined in Control.Carrier.Empty.Church Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (EmptyC m) -> (Empty :+: sig) n a -> ctx () -> EmptyC m (ctx a) Source #
Algebra sig m => Algebra (Empty :+: sig) (EmptyC m) Source #
Instance details Defined in Control.Carrier.Empty.Maybe Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (EmptyC m) -> (Empty :+: sig) n a -> ctx () -> EmptyC m (ctx a) Source #
Algebra sig m => Algebra (Empty :+: sig) (MaybeT m) Source #
Instance details Defined in Control.Algebra Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (MaybeT m) -> (Empty :+: sig) n a -> ctx () -> MaybeT m (ctx a) Source #
Algebra sig m => Algebra (Fail :+: sig) (FailC m) Source #
Instance details Defined in Control.Carrier.Fail.Either Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (FailC m) -> (Fail :+: sig) n a -> ctx () -> FailC m (ctx a) Source #
Algebra sig m => Algebra (Fresh :+: sig) (FreshC m) Source #
Instance details Defined in Control.Carrier.Fresh.Church Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (FreshC m) -> (Fresh :+: sig) n a -> ctx () -> FreshC m (ctx a) Source #
Algebra sig m => Algebra (Fresh :+: sig) (FreshC m) Source #
Instance details Defined in Control.Carrier.Fresh.Strict Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (FreshC m) -> (Fresh :+: sig) n a -> ctx () -> FreshC m (ctx a) Source #
Algebra sig m => Algebra (NonDet :+: sig) (NonDetC m) Source #
Instance details Defined in Control.Carrier.NonDet.Church Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (NonDetC m) -> (NonDet :+: sig) n a -> ctx () -> NonDetC m (ctx a) Source #
Algebra sig m => Algebra (Trace :+: sig) (TraceC m) Source #
Instance details Defined in Control.Carrier.Trace.Ignoring Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (TraceC m) -> (Trace :+: sig) n a -> ctx () -> TraceC m (ctx a) Source #
(MonadIO m, Algebra sig m) => Algebra (Trace :+: sig) (TraceC m) Source #
Instance details Defined in Control.Carrier.Trace.Printing Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (TraceC m) -> (Trace :+: sig) n a -> ctx () -> TraceC m (ctx a) Source #
Algebra sig m => Algebra (Trace :+: sig) (TraceC m) Source #
Instance details Defined in Control.Carrier.Trace.Returning Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (TraceC m) -> (Trace :+: sig) n a -> ctx () -> TraceC m (ctx a) Source #
Algebra sig m => Algebra (Error e :+: sig) (ErrorC e m) Source #
Instance details Defined in Control.Carrier.Error.Church Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (ErrorC e m) -> (Error e :+: sig) n a -> ctx () -> ErrorC e m (ctx a) Source #
Algebra sig m => Algebra (Error e :+: sig) (ErrorC e m) Source #
Instance details Defined in Control.Carrier.Error.Either Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (ErrorC e m) -> (Error e :+: sig) n a -> ctx () -> ErrorC e m (ctx a) Source #
Algebra sig m => Algebra (Error e :+: sig) (ExceptT e m) Source #
Instance details Defined in Control.Algebra Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (ExceptT e m) -> (Error e :+: sig) n a -> ctx () -> ExceptT e m (ctx a) Source #
Algebra sig m => Algebra (Reader r :+: sig) (ReaderC r m) Source #
Instance details Defined in Control.Carrier.Reader Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (ReaderC r m) -> (Reader r :+: sig) n a -> ctx () -> ReaderC r m (ctx a) Source #
Algebra sig m => Algebra (Reader r :+: sig) (ReaderT r m) Source #
Instance details Defined in Control.Algebra Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (ReaderT r m) -> (Reader r :+: sig) n a -> ctx () -> ReaderT r m (ctx a) Source #
Algebra sig m => Algebra (State s :+: sig) (StateC s m) Source #
Instance details Defined in Control.Carrier.State.Church Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (StateC s m) -> (State s :+: sig) n a -> ctx () -> StateC s m (ctx a) Source #
Algebra sig m => Algebra (State s :+: sig) (StateC s m) Source #
Instance details Defined in Control.Carrier.State.Lazy Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (StateC s m) -> (State s :+: sig) n a -> ctx () -> StateC s m (ctx a) Source #
Algebra sig m => Algebra (State s :+: sig) (StateC s m) Source #
Instance details Defined in Control.Carrier.State.Strict Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (StateC s m) -> (State s :+: sig) n a -> ctx () -> StateC s m (ctx a) Source #
Algebra sig m => Algebra (State s :+: sig) (StateT s m) Source #
Instance details Defined in Control.Algebra Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (StateT s m) -> (State s :+: sig) n a -> ctx () -> StateT s m (ctx a) Source #
Algebra sig m => Algebra (State s :+: sig) (StateT s m) Source #
Instance details Defined in Control.Algebra Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (StateT s m) -> (State s :+: sig) n a -> ctx () -> StateT s m (ctx a) Source #
Algebra sig m => Algebra (Throw e :+: sig) (ThrowC e m) Source #
Instance details Defined in Control.Carrier.Throw.Either Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (ThrowC e m) -> (Throw e :+: sig) n a -> ctx () -> ThrowC e m (ctx a) Source #
(Algebra sig m, Monoid w) => Algebra (Writer w :+: sig) (WriterC w m) Source #
Instance details Defined in Control.Carrier.Writer.Church Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (WriterC w m) -> (Writer w :+: sig) n a -> ctx () -> WriterC w m (ctx a) Source #
(Monoid w, Algebra sig m) => Algebra (Writer w :+: sig) (WriterC w m) Source #
Instance details Defined in Control.Carrier.Writer.Strict Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (WriterC w m) -> (Writer w :+: sig) n a -> ctx () -> WriterC w m (ctx a) Source #
(Algebra sig m, Monoid w) => Algebra (Writer w :+: sig) (WriterT w m) Source #
Instance details Defined in Control.Algebra Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (WriterT w m) -> (Writer w :+: sig) n a -> ctx () -> WriterT w m (ctx a) Source #
(Algebra sig m, Monoid w) => Algebra (Writer w :+: sig) (WriterT w m) Source #
Instance details Defined in Control.Algebra Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (WriterT w m) -> (Writer w :+: sig) n a -> ctx () -> WriterT w m (ctx a) Source #
(Algebra sig m, Monoid w) => Algebra (Writer w :+: sig) (WriterT w m) Source #
Instance details Defined in Control.Algebra Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (WriterT w m) -> (Writer w :+: sig) n a -> ctx () -> WriterT w m (ctx a) Source #
(Reifies s (Interpreter eff m), Algebra sig m) => Algebra (eff :+: sig) (InterpretC s eff m) Source #
Instance details Defined in Control.Carrier.Interpret Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (InterpretC s eff m) -> (eff :+: sig) n a -> ctx () -> InterpretC s eff m (ctx a) Source #
Algebra (eff :+: sig) (sub m) => Algebra (Labelled label eff :+: sig) (Labelled label sub m) Source #
Instance details Defined in Control.Effect.Labelled Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (Labelled label sub m) -> (Labelled label eff :+: sig) n a -> ctx () -> Labelled label sub m (ctx a) Source #
(Algebra sig m, Monoid w) => Algebra (Reader r :+: (Writer w :+: (State s :+: sig))) (RWST r w s m) Source #
Instance details Defined in Control.Algebra Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (RWST r w s m) -> (Reader r :+: (Writer w :+: (State s :+: sig))) n a -> ctx () -> RWST r w s m (ctx a) Source #
(Algebra sig m, Monoid w) => Algebra (Reader r :+: (Writer w :+: (State s :+: sig))) (RWST r w s m) Source #
Instance details Defined in Control.Algebra Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (RWST r w s m) -> (Reader r :+: (Writer w :+: (State s :+: sig))) n a -> ctx () -> RWST r w s m (ctx a) Source #
(Algebra sig m, Monoid w) => Algebra (Reader r :+: (Writer w :+: (State s :+: sig))) (RWST r w s m) Source #
Instance details Defined in Control.Algebra Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (RWST r w s m) -> (Reader r :+: (Writer w :+: (State s :+: sig))) n a -> ctx () -> RWST r w s m (ctx a) Source #
(LabelledMember label sub sig, Algebra sig m) => Algebra (sub :+: sig) (UnderLabel label sub m) Source #
Instance details Defined in Control.Effect.Labelled Methods alg :: forall ctx (n :: Type -> Type) a. Functor ctx => Handler ctx n (UnderLabel label sub m) -> (sub :+: sig) n a -> ctx () -> UnderLabel label sub m (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.

Since: 1.0.0.0

run :: Identity a -> a Source #

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

Since: 1.0.0.0