Safe Haskell | Safe-Inferred |
---|---|
Language | Haskell2010 |
An effect allowing writes to an accumulated quantity alongside a computed value,
and reads from the accumulator.
An Accum
w
effect keeps track of a monoidal datum of type w
and strictly appends to that monoidal value with the add
effect.
Previous writes to that value can be read with the look
effect.
Predefined carriers:
- Control.Carrier.Accum.Church
- Control.Carrier.Accum.Strict. (A lazy carrier is not provided due to the inherent space leaks associated with lazy accumulation monads, similar to lazy writer monads.)
- Control.Monad.Trans.Accum
If Accum
w
is the last effect in a stack, it can be interpreted to a function w -> (w, a)
given some result type a
and the presence of a Monoid
instance for w
.
- - | @since 1.1.2.0
Accumulation effect
data Accum w (m :: Type -> Type) k where Source #
Since: 1.1.2.0
Instances
(Algebra sig m, Monoid w) => Algebra (Accum w :+: sig) (AccumC w m) Source # | |
(Algebra sig m, Semigroup w, MonadIO m) => Algebra (Accum w :+: sig) (AccumC w m) Source # | |
(Algebra sig m, Monoid w) => Algebra (Accum w :+: sig) (AccumC w m) Source # | |
(Algebra sig m, Monoid w) => Algebra (Accum w :+: sig) (AccumT w m) Source # | |
looks :: Has (Accum w) sig m => (w -> a) -> m a Source #
Look up the previous accumulation and apply a function to it.
looks f = fmap f look
Since: 1.1.2.0
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
Instances
Algebra Choose NonEmpty Source # | |
Algebra Empty Maybe Source # | |
Algebra NonDet [] Source # | |
Algebra sig m => Algebra sig (Choosing m) Source # | |
Algebra sig m => Algebra sig (Ap m) Source # | This instance permits effectful actions to be lifted into the mappend <$> act1 <*> (mappend <$> act2 <*> act3) is equivalent to getAp (act1 <> act2 <> act3) Since: 1.0.1.0 |
Algebra sig m => Algebra sig (Alt m) Source # | This instance permits effectful actions to be lifted into the a <|> b <|> c <|> d is equivalent to getAlt (mconcat [a, b, c, d]) Since: 1.0.1.0 |
Algebra sig m => Algebra sig (IdentityT m) Source # | |
Algebra (Lift Identity) Identity Source # | |
Algebra (Lift IO) IO Source # | |
Algebra (Error e) (Either e) Source # | |
Monad m => Algebra (Lift m) (LiftC m) Source # | |
Monoid w => Algebra (Writer w) ((,) w) Source # | |
Algebra (Reader r) ((->) r) Source # | |
Algebra sig m => Algebra (Choose :+: sig) (ChooseC m) Source # | |
Algebra sig m => Algebra (Cull :+: (NonDet :+: sig)) (CullC m) Source # | |
Algebra sig m => Algebra (Cut :+: (NonDet :+: sig)) (CutC m) Source # | |
Algebra sig m => Algebra (Empty :+: sig) (EmptyC m) Source # | |
Algebra sig m => Algebra (Empty :+: sig) (EmptyC m) Source # | |
Algebra sig m => Algebra (Empty :+: sig) (MaybeT m) Source # | |
Algebra sig m => Algebra (Fail :+: sig) (FailC m) Source # | |
Algebra sig m => Algebra (Fresh :+: sig) (FreshC m) Source # | |
Algebra sig m => Algebra (Fresh :+: sig) (FreshC m) Source # | |
Algebra sig m => Algebra (NonDet :+: sig) (NonDetC m) Source # | |
Algebra sig m => Algebra (Trace :+: sig) (TraceC m) Source # | |
(MonadIO m, Algebra sig m) => Algebra (Trace :+: sig) (TraceC m) Source # | |
Algebra sig m => Algebra (Trace :+: sig) (TraceC m) Source # | |
(Algebra sig m, Monoid w) => Algebra (Accum w :+: sig) (AccumC w m) Source # | |
(Algebra sig m, Semigroup w, MonadIO m) => Algebra (Accum w :+: sig) (AccumC w m) Source # | |
(Algebra sig m, Monoid w) => Algebra (Accum w :+: sig) (AccumC w m) Source # | |
(Algebra sig m, Monoid w) => Algebra (Accum w :+: sig) (AccumT w m) Source # | |
Algebra sig m => Algebra (Error e :+: sig) (ErrorC e m) Source # | |
Algebra sig m => Algebra (Error e :+: sig) (ErrorC e m) Source # | |
Algebra sig m => Algebra (Error e :+: sig) (ExceptT e m) Source # | |
Algebra sig m => Algebra (Reader r :+: sig) (ReaderC r m) Source # | |
Algebra sig m => Algebra (Reader r :+: sig) (ReaderT r m) Source # | |
Algebra sig m => Algebra (State s :+: sig) (StateC s m) Source # | |
(MonadIO m, Algebra sig m) => Algebra (State s :+: sig) (StateC s m) Source # | |
Algebra sig m => Algebra (State s :+: sig) (StateC s m) Source # | |
Algebra sig m => Algebra (State s :+: sig) (StateC s m) Source # | |
Algebra sig m => Algebra (State s :+: sig) (StateT s m) Source # | |
Algebra sig m => Algebra (State s :+: sig) (StateT s m) Source # | |
Algebra sig m => Algebra (Throw e :+: sig) (ThrowC e m) Source # | |
(Algebra sig m, Monoid w) => Algebra (Writer w :+: sig) (WriterC w m) Source # | |
(Monoid w, Algebra sig m) => Algebra (Writer w :+: sig) (WriterC w m) Source # | |
(Algebra sig m, Monoid w) => Algebra (Writer w :+: sig) (WriterT w m) Source # | |
(Algebra sig m, Monoid w) => Algebra (Writer w :+: sig) (WriterT w m) Source # | |
(Algebra sig m, Monoid w) => Algebra (Writer w :+: sig) (WriterT w m) Source # | |
(Reifies s (Interpreter eff m), Algebra sig m) => Algebra (eff :+: sig) (InterpretC s eff m) Source # | |
Defined in Control.Carrier.Interpret 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 # | |
(Algebra sig m, Monoid w) => Algebra (Reader r :+: (Writer w :+: (State s :+: sig))) (RWST r w s m) Source # | |
(Algebra sig m, Monoid w) => Algebra (Reader r :+: (Writer w :+: (State s :+: sig))) (RWST r w s m) Source # | |
(Algebra sig m, Monoid w) => Algebra (Reader r :+: (Writer w :+: (State s :+: sig))) (RWST r w s m) Source # | |
(LabelledMember label sub sig, Algebra sig m) => Algebra (sub :+: sig) (UnderLabel label sub m) Source # | |
Defined in Control.Effect.Labelled 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