drinkery

drinkery is a yet another stream processing library themed on liquors. While it offers a simple interface, it also tries to be as expressive as possible.

Producers

drinkery supports three types of producers: Producer, ListT, and Tap.

Producer r s is a monad transformer to produce a stream of type s. It is good at interactively serving values. yield :: s -> Producer r s m a is the primary action. A barman can also accept requests from the downstream using accept.

ListT r is a list-like backtracking monad (also known as ListT done right). It is useful for sampling elements of containers with effects. sample :: Foldable f => f s -> ListT r m s samples elements in any Foldable container. inquire to interact with the downstream.

Tap is an endless producer. This can be connected to a ‘Patron’ or a ‘Distiller’.

Producer and ListT are converted to Tap by runProducer and runListT respectively.

Consumer

Sink tap is a monad transformer which consumes tap.

• drink :: m s Get one element.
• leftover :: s -> m () Leave one element.
• request :: r -> m () Send a request.

(+&) :: (Monoid r, CloseRequest r, Monad m) => Tap r s m -> Sink (Tap r s) m a -> m a connects a tap with a drinker.

Transducer

Distiller tap m r s is a stream transducer which

• Consumes tap
• Receives r
• Produces s

It is actually a Tap where the underlying monad is Sink.

There are two composition operators:

• ++& Tap-drinker
• ++$ Tap-distiller

+, &, and $ means a tap, a drinker, and a distiller respectively. The middle characters of these operators signify the resulting structures.

Why drinkery?

drinkery is designed to be fully featured and complements other libraries’ missing functionalities.

pipes

pipes is quite similar in that both Proxy and Distiller are bidirectional. Still there are some differences:

• Distiller does not terminate.
• Unlike pipes’ >->, ++$ propagates inner requests:
  • (++$) :: Monad m => Distiller tap m p q -> Distiller (Tap p q) (Sink tap m) r s -> Distiller tap m r s
  • (>->) :: Proxy a' a () b m r -> Proxy () b c' c m r -> Proxy a' a c' c m r
• Sink, the consumer monad, may leave unconsumed inputs.
• drinkery has much fewer operators.

conduit

Both drinkery and conduit support leftovers, closing operation, and end of stream. The main difference is interactivity.

machines

machines does not support leftovers, nor interactive producers. Both machines and drinkery support multi-channel input.

iteratee

iteratee has an ability to handle requests but those are untyped (SomeException). drinkery provides a more robust interface for handling requests, and monadic producers.