Dep.Advice.Basic

This module contains basic examples advices.

BEWARE! These are provided for illustrative purposes only, they strive for simplicity and not robustness or efficiency.

Basic advices

doLocally :: forall ca e_ m r. Monad m => (e_ (DepT e_ m) -> e_ (DepT e_ m)) -> Advice ca e_ m r

Use local on the final DepT action of a function.

Allows tweaking the environment that will be seen by the function and all of its sub-calls into dependencies.

Perhaps this is not what you want; often, it's better to tweak the environment for the current function only. For those cases, deceive might be a better fit.

>>> :{
 type HasLogger :: Type -> (Type -> Type) -> Constraint
 class HasLogger em m | em -> m where
   logger :: em -> String -> m ()
 type Env :: (Type -> Type) -> Type
 data Env m = Env
   { _logger1 :: String -> m (),
     _logger2 :: String -> m (),
     _controllerA :: Int -> m (),
     _controllerB :: Int -> m ()
   }
 instance HasLogger (Env m) m where
   logger = _logger1
 envIO :: Env (DepT Env IO)
 envIO = Env 
   {
     _logger1 = 
         \_ -> liftIO $ putStrLn "logger1 ran",
     _logger2 = 
         \_ -> liftIO $ putStrLn "logger2 ran",
     _controllerA = 
         \_ -> do e <- ask; logger e "foo",
     _controllerB = 
         advise @Top 
         (doLocally \e@Env{_logger2} -> e {_logger1 = _logger2}) 
         \_ -> do e <- ask; logger e "foo" 
   }
:}

>>> runFromEnv (pure envIO) _controllerA 0
logger1 ran

>>> runFromEnv (pure envIO) _controllerB 0
logger2 ran