| Safe Haskell | Safe |
|---|---|
| Language | Haskell2010 |
Control.Eff.Reader.Strict
Description
Strict read-only state
Synopsis
- data Reader (e :: k) (v :: k) where
- withReader :: Monad m => a -> e -> m a
- ask :: forall e (r :: [Type -> Type]). Member (Reader e) r => Eff r e
- local :: forall e a (r :: [Type -> Type]). Member (Reader e) r => (e -> e) -> Eff r a -> Eff r a
- reader :: forall e (r :: [Type -> Type]) a. Member (Reader e) r => (e -> a) -> Eff r a
- runReader :: forall e (r :: [Type -> Type]) w. e -> Eff (Reader e ': r) w -> Eff r w
Documentation
data Reader (e :: k) (v :: k) where Source #
The Reader monad
The request for a value of type e from the current environment
This can be expressed as a GADT because the type of values
returned in response to a (Reader e a) request is not any a;
we expect in reply the value of type e, the value from the
environment. So, the return type is restricted: 'a ~ e'
One can also define this as
data Reader e v = (e ~ v) => Reader
^ without GADTs, using explicit coercion as is done here.
newtype Reader e v = Reader (e->v)
^ In the latter case, when we make the request, we make it as Reader id. So, strictly speaking, GADTs are not really necessary.
Instances
| (MonadBase m m, LiftedBase m s) => MonadBaseControl m (Eff (Reader e ': s)) Source # | |
| Handle (Reader e) r a (e -> k) Source # | Given a value to read, and a callback, how to respond to requests. |
Defined in Control.Eff.Reader.Strict Methods handle :: (Eff r a -> e -> k) -> Arrs r v a -> Reader e v -> e -> k Source # handle_relay :: forall (r' :: [Type -> Type]). (r ~ (Reader e ': r'), Relay (e -> k) r') => (a -> e -> k) -> (Eff r a -> e -> k) -> Eff r a -> e -> k Source # respond_relay :: (a -> e -> k) -> (Eff r a -> e -> k) -> Eff r a -> e -> k Source # | |
| type StM (Eff (Reader e ': s)) a Source # | |
withReader :: Monad m => a -> e -> m a Source #
How to interpret a pure value in a reader context
ask :: forall e (r :: [Type -> Type]). Member (Reader e) r => Eff r e Source #
Get the current value from a Reader. The signature is inferred (when using NoMonomorphismRestriction).
local :: forall e a (r :: [Type -> Type]). Member (Reader e) r => (e -> e) -> Eff r a -> Eff r a Source #
Locally rebind the value in the dynamic environment This function is like a relay; it is both an admin for Reader requests, and a requestor of them.