Pipes by Example

Presented to YOW! Lambda Jam 2014.

Transcript

1. Pipes by Example Nick Partridge. nkpart on most things.
2. Why Pipes Because you’re writing a web server, of course.
3. Not just for streaming! produce :: m a consume :: a -> m ()
4. Pipe Types Lead, PVC, etc.
5. Producers Consumers + Pipes Proxy a a’ b b’ m c
6. Pipe a b m r a b m On exhaustion: r Proxy () a () b m r
7. Producer b m r _ b m On exhaustion: r Proxy X () () b m r
8. Consumer a m r a _ m On exhaustion: r Proxy () a () X m r
9. The Primitives Because live coding always works.
10. Use the Monad Running producers sequentially is just >> When pipes/consumers/producers/finish, they return a value Control.Monad and friends are very useful.
11. Elimination Finally some Category Theory.
12. Pipe a b m r a b m On exhaustion: r
13. Effect m r m On exhaustion: r _ _ Proxy X () () X m r
14. Substitution Producers: for or ~> eliminates yield Consumer side: >~ eliminates await
15. Elimination - Loop Bodies for generator body ! for x yield == x for (yield x) f == f x
16. Companion Libraries Where the features are hiding.
17. Companion Libraries pipes-parse pipes-safe pipes-group
18. 1. Pipes Parse type Parser a m r = forall x. StateT (Producer a m x) m r Provides ‘push-back’. You can modify the underlying producer to return a value again.
19. 2. Pipes Safe ReaderT (IORef (Finalizers m)) m r Resource management, exception safety, through a monad transformer on m that allows registering Finalizers.
20. 3. Pipes Group FreeT (Producer a m) m x Working on sub-streams in constant memory. a ‘linked-list’ of sub-stream producers, each one returning the next sub-stream on exhaustion
21. return () :: Effect Talk ()
22. References Pipes haddocks - Pipes, Pipes.Prelude, Pipes.Tutorial Haskell for All - Gabriel Gonzales’ blog Haskell Pipes Google Group “pipes-“ seach on hackage