| Safe Haskell | Safe |
|---|---|
| Language | Haskell2010 |
Control.Eff.Reader.Strict
Description
Strict read-only state
Documentation
data Reader e v 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.
ask :: 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. 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