Control.Monad.Reader.Class

class MonadAsk :: Type -> (Type -> Type) -> Constraintclass (Monad m) <= MonadAsk r m | m -> r where

The MonadAsk type class represents those monads which support a global context that can be provided via the ask function.

An implementation is provided for ReaderT, and for other monad transformers defined in this library.

Law:

• do { ask ; ask } = ask

Members

• ask :: m r

Instances

• MonadAsk r (Function r)

asks :: forall r m a. MonadAsk r m => (r -> a) -> m a

Projects a value from the global context in a MonadAsk.

class MonadReader :: Type -> (Type -> Type) -> Constraintclass (MonadAsk r m) <= MonadReader r m | m -> r where

An extension of the MonadAsk class that introduces a function local f x that allows the value of the local context to be modified for the duration of the execution of action x.

An implementation is provided for ReaderT, and for other monad transformers defined in this library.

Laws in addition to the MonadAsk law:

• local f ask = f <$> ask
• local _ (pure a) = pure a
• local f (do { a <- x ; y }) = do { a <- local f x ; local f y }

Members

• local :: forall a. (r -> r) -> m a -> m a

Instances

• MonadReader r (Function r)