Orville.PostgreSQL.Monad.HasOrvilleState

Since: 1.0.0.0

Documentation

class HasOrvilleState m where

HasOrvilleState is the typeclass that Orville uses to access and manange the connection pool and state tracking when it is being executed inside an unknown Monad. It is a specialized version of the Reader interface so that it can be easily implemented by application Monads that already have a Reader context and want to simply add OrvilleState as an attribute to that context, like so

   data MyApplicationState =
     MyApplicationState
       { appConfig :: MyAppConfig
       , appOrvilleState :: OrvilleState
       }

   newtype MyApplicationMonad a =
     MyApplicationMonad (ReaderT MyApplicationState IO) a

   instance HasOrvilleState MyApplicationMonad where
     askOrvilleState =
       MyApplicationMonad (asks appOrvilleState)

     localOrvilleState f (MyApplicationMonad reader) =
       MyApplicationMonad $
         local
           (\state -> state { appOrvilleState = f (appOrvilleState state))
           reader
 

An instance for 'ReaderT OrvilleState m' is provided as a convenience in the case that your application has no extra context to track.

Since: 1.0.0.0

Methods

askOrvilleState :: m OrvilleState

Fetches the current OrvilleState from the host Monad context. The equivalent of ask for 'ReaderT OrvilleState'.

Since: 1.0.0.0

localOrvilleState

Arguments

:: (OrvilleState -> OrvilleState)

The function to modify the OrvilleState.

-> m a

The monad operation to execute with the modified state.

-> m a

Applies a modification to the OrvilleState that is local to the given monad operation. Calls to askOrvilleState made within the 'm a' provided must return the modified state. The modified state must only apply to the given 'm a' and not be persisted beyond it. The equivalent of local for 'ReaderT OrvilleState'.

Since: 1.0.0.0

Instances

HasOrvilleState Orville

Defined in Orville.PostgreSQL.Monad.Orville

Methods

askOrvilleState :: Orville OrvilleState

localOrvilleState :: (OrvilleState -> OrvilleState) -> Orville a -> Orville a

Monad m => HasOrvilleState (ReaderT OrvilleState m)

Defined in Orville.PostgreSQL.Monad.HasOrvilleState

Methods

askOrvilleState :: ReaderT OrvilleState m OrvilleState

localOrvilleState :: (OrvilleState -> OrvilleState) -> ReaderT OrvilleState m a -> ReaderT OrvilleState m a

(Monad m, HasOrvilleState m) => HasOrvilleState (ReaderT r m)

Defined in Orville.PostgreSQL.Monad.HasOrvilleState

Methods

askOrvilleState :: ReaderT r m OrvilleState

localOrvilleState :: (OrvilleState -> OrvilleState) -> ReaderT r m a -> ReaderT r m a