| Safe Haskell | None |
|---|---|
| Language | Haskell2010 |
Control.Effect.Lift
Contents
Description
Synopsis
- data Lift sig m k = LiftWith (forall ctx. Functor ctx => ctx () -> (forall a. ctx (m a) -> sig (ctx a)) -> sig (ctx a)) (a -> m k)
- sendM :: (Has (Lift n) sig m, Functor n) => n a -> m a
- liftWith :: Has (Lift n) sig m => (forall ctx. Functor ctx => ctx () -> (forall a. ctx (m a) -> n (ctx a)) -> n (ctx a)) -> m a
- class (HFunctor sig, Monad m) => Algebra sig m | m -> sig
- type Has eff sig m = (Members eff sig, Algebra sig m)
- run :: Identity a -> a
Lift effect
Since: 1.0.0.0
Constructors
| LiftWith (forall ctx. Functor ctx => ctx () -> (forall a. ctx (m a) -> sig (ctx a)) -> sig (ctx a)) (a -> m k) |
sendM :: (Has (Lift n) sig m, Functor n) => n a -> m a Source #
Given a Lift n constraint in a signature carried by m, sendM
promotes arbitrary actions of type n a to m a. It is spiritually
similar to lift from the MonadTrans typeclass.
Since: 1.0.0.0
liftWith :: Has (Lift n) sig m => (forall ctx. Functor ctx => ctx () -> (forall a. ctx (m a) -> n (ctx a)) -> n (ctx a)) -> m a Source #
Run actions in an outer context.
This can be used to provide interoperation with base functionality like Control.Exception.:catch
liftWith$ ctx hdl ->catch(hdl (m <$ ctx)) (hdl . (<$ ctx) . h)
The higher-order function takes both an initial context, and a handler phrased as the same sort of distributive law as described in the documentation for thread. This handler takes actions lifted into a context functor, which can be either the initial context, or the derived context produced by handling a previous action.
As with MonadBaseControl, care must be taken when lifting functions like Control.Exception. which don’t use the return value of one of their actions, as this can lead to dropped effects.finally
Since: 1.0.0.0
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
Instances
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.