viking

The Vikings were daring masters of the sea. The shallow draught of their swift wooden longships meant that they were able to reach far inland by river and stream, striking and moving on before local forces could muster.

Overview

Viking is an opinionated wrapper around michaelt's streaming and streaming-bytestring libraries. The motivation is twofold, to rename some problematic data types and modules so that usage is a bit more seamless, and to provide additional functionality on top in an x- like fashion. In particular, functions which throw exceptions are replaced with ones which expose errors in EitherT.

Alternatives

Viking, and indeed the streaming library, differs from libraries like conduit and pipes in that it models streams as lists rather than list transformers.

Using the analogy of pure lists, you can think of a Conduit a m b as a function from [a] -> [b], a Source m a can be thought of as a [a] and a Sink m b can be thought of as a [b] -> (). In Viking on the other hand, a Stream (Of a) m () is equivalent to a [a], and everything else is just functions. The implication of this is that writing streaming operations with Viking feels a lot like programming with lists.

For example, if you wanted to write a function which adds one to an integer stream and then turns it into a string:

Data.List

transform :: [Int] -> [String]
transform =
  fmap show . fmap (+ 1)

Viking

transform :: Monad m => Stream (Of Int) m r -> Stream (Of String) m r
transform =
  Stream.map show . Stream.map (+ 1)

Conduit

transform :: Monad m => Conduit Int m String
transform =
  Conduit.map (+ 1) =$= Conduit.map show