Safe Haskell | None |
---|---|
Language | Haskell2010 |
Synopsis
- newtype Final m z a where
- WithWeavingToFinal :: ThroughWeavingToFinal m z a -> Final m z a
- type ThroughWeavingToFinal m z a = forall f. Functor f => f () -> (forall x. f (z x) -> m (f x)) -> (forall x. f x -> Maybe x) -> m (f a)
- withWeavingToFinal :: forall m r a. Member (Final m) r => ThroughWeavingToFinal m (Sem r) a -> Sem r a
- withStrategicToFinal :: Member (Final m) r => Strategic m (Sem r) a -> Sem r a
- embedFinal :: (Member (Final m) r, Functor m) => m a -> Sem r a
- interpretFinal :: forall m e r a. Member (Final m) r => (forall x rInitial. e (Sem rInitial) x -> Strategic m (Sem rInitial) x) -> Sem (e ': r) a -> Sem r a
- type Strategic m n a = forall f. Functor f => Sem (WithStrategy m f n) (m (f a))
- type WithStrategy m f n = '[Strategy m f n]
- pureS :: Applicative m => a -> Strategic m n a
- liftS :: Functor m => m a -> Strategic m n a
- runS :: n a -> Sem (WithStrategy m f n) (m (f a))
- bindS :: (a -> n b) -> Sem (WithStrategy m f n) (f a -> m (f b))
- getInspectorS :: forall m f n. Sem (WithStrategy m f n) (Inspector f)
- getInitialStateS :: forall m f n. Sem (WithStrategy m f n) (f ())
- runFinal :: Monad m => Sem '[Final m] a -> m a
- finalToFinal :: forall m1 m2 r a. Member (Final m2) r => (forall x. m1 x -> m2 x) -> (forall x. m2 x -> m1 x) -> Sem (Final m1 ': r) a -> Sem r a
- embedToFinal :: (Member (Final m) r, Functor m) => Sem (Embed m ': r) a -> Sem r a
Effect
newtype Final m z a where Source #
An effect for embedding higher-order actions in the final target monad of the effect stack.
This is very useful for writing interpreters that interpret higher-order effects in terms of the final monad.
Final
is more powerful than Embed
, but is also less flexible
to interpret (compare runEmbedded
with finalToFinal
).
If you only need the power of embed
, then you should use Embed
instead.
Beware: Final
actions are interpreted as actions of the final monad,
and the effectful state visible to
withWeavingToFinal
/ withStrategicToFinal
/ interpretFinal
is that of all interpreters run in order to produce the final monad.
This means that any interpreter built using Final
will not
respect local/global state semantics based on the order of
interpreters run. You should signal interpreters that make use of
Final
by adding a -
suffix to the names of these.Final
State semantics of effects that are not interpreted in terms of the final monad will always appear local to effects that are interpreted in terms of the final monad.
State semantics between effects that are interpreted in terms of the final monad depend on the final monad. For example, if the final monad is a monad transformer stack, then state semantics will depend on the order monad transformers are stacked.
Since: 1.2.0.0
WithWeavingToFinal :: ThroughWeavingToFinal m z a -> Final m z a |
type ThroughWeavingToFinal m z a = forall f. Functor f => f () -> (forall x. f (z x) -> m (f x)) -> (forall x. f x -> Maybe x) -> m (f a) Source #
This represents a function which produces
an action of the final monad m
given:
- The initial effectful state at the moment the action is to be executed.
- A way to convert
z
(which is typically
) toSem
rm
by threading the effectful state through. - An inspector that is able to view some value within the effectful state if the effectful state contains any values.
A
provides these components,
hence the name Weaving
ThroughWeavingToFinal
.
Since: 1.2.0.0
Actions
withWeavingToFinal :: forall m r a. Member (Final m) r => ThroughWeavingToFinal m (Sem r) a -> Sem r a Source #
Allows for embedding higher-order actions of the final monad
by providing the means of explicitly threading effects through
to the final monad.Sem
r
Consider using withStrategicToFinal
instead,
which provides a more user-friendly interface, but is also slightly weaker.
You are discouraged from using withWeavingToFinal
directly
in application code, as it ties your application code directly to
the final monad.
Since: 1.2.0.0
withStrategicToFinal :: Member (Final m) r => Strategic m (Sem r) a -> Sem r a Source #
Allows for embedding higher-order actions of the final monad
by providing the means of explicitly threading effects through
to the final monad. This is done through the use of the Sem
rStrategic
environment, which provides runS
and bindS
.
You are discouraged from using withStrategicToFinal
in application code,
as it ties your application code directly to the final monad.
Since: 1.2.0.0
embedFinal :: (Member (Final m) r, Functor m) => m a -> Sem r a Source #
withWeavingToFinal
admits an implementation of embed
.
Just like embed
, you are discouraged from using this in application code.
Since: 1.2.0.0
Combinators for Interpreting to the Final Monad
:: forall m e r a. Member (Final m) r | |
=> (forall x rInitial. e (Sem rInitial) x -> Strategic m (Sem rInitial) x) | A natural transformation from the handled effect to the final monad. |
-> Sem (e ': r) a | |
-> Sem r a |
Like interpretH
, but may be used to
interpret higher-order effects in terms of the final monad.
interpretFinal
requires less boilerplate than using interpretH
together with withStrategicToFinal
/ withWeavingToFinal
,
but is also less powerful.
interpretFinal
does not provide any means of executing actions
of
as you interpret each action, and the provided interpreter
is automatically recursively used to process higher-order occurences of
Sem
r
to Sem
(e ': r)
.Sem
r
If you need greater control of how the effect is interpreted,
use interpretH
together with withStrategicToFinal
/
withWeavingToFinal
instead.
Beware: Effects that aren't interpreted in terms of the final
monad will have local state semantics in regards to effects
interpreted using interpretFinal
. See Final
.
Since: 1.2.0.0
Strategy
Strategy is a domain-specific language very similar to Tactics
(see Tactical
), and is used to describe how higher-order
effects are threaded down to the final monad.
Much like Tactics
, computations can be run and threaded
through the use of runS
and bindS
, and first-order constructors
may use pureS
. In addition, liftS
may be used to
lift actions of the final monad.
Unlike Tactics
, the final return value within a Strategic
must be a monadic value of the target monad
with the functorial state wrapped inside of it.
type WithStrategy m f n = '[Strategy m f n] Source #
Since: 1.2.0.0
liftS :: Functor m => m a -> Strategic m n a Source #
Lifts an action of the final monad into Strategic
.
Note: you don't need to use this function if you already have a monadic
action with the functorial state threaded into it, by the use of
runS
or bindS
.
In these cases, you need only use pure
to embed the action into the
Strategic
environment.
Since: 1.2.0.0
runS :: n a -> Sem (WithStrategy m f n) (m (f a)) Source #
Lifts a monadic action into the stateful environment, in terms
of the final monad.
The stateful environment will be the same as the one that the Strategy
is initially run in.
Use bindS
if you'd prefer to explicitly manage your stateful environment.
Since: 1.2.0.0
bindS :: (a -> n b) -> Sem (WithStrategy m f n) (f a -> m (f b)) Source #
getInspectorS :: forall m f n. Sem (WithStrategy m f n) (Inspector f) Source #
Get a natural transformation capable of potentially inspecting values
inside of f
. Binding the result of getInspectorS
produces a function that
can sometimes peek inside values returned by bindS
.
This is often useful for running callback functions that are not managed by polysemy code.
See also getInspectorT
Since: 1.2.0.0
getInitialStateS :: forall m f n. Sem (WithStrategy m f n) (f ()) Source #
Interpretations
runFinal :: Monad m => Sem '[Final m] a -> m a Source #
Lower a Sem
containing only a single lifted, final Monad
into that
monad.
If you also need to process an
effect, use this together with
Embed
membedToFinal
.
Since: 1.2.0.0
finalToFinal :: forall m1 m2 r a. Member (Final m2) r => (forall x. m1 x -> m2 x) -> (forall x. m2 x -> m1 x) -> Sem (Final m1 ': r) a -> Sem r a Source #