Pipes by Example Nick Partridge. nkpart on most things. Why Pipes - PowerPoint PPT Presentation

Pipes by Example Nick Partridge. nkpart on most things.

Why Pipes Because you’re writing a web server, of course.

Not just for streaming! produce :: m a consume :: a -> m ()

Pipe Types Lead, PVC, etc.

Producers + Consumers Pipes Proxy a a’ b b’ m c

m a b Pipe a b m r On exhaustion: r Proxy () a () b m r

m _ b Producer b m r On exhaustion: r Proxy X () () b m r

m a _ Consumer a m r On exhaustion: r Proxy () a () X m r

The Primitives Because live coding always works.

Use the Monad Running producers sequentially is just >> When pipes/consumers/producers/finish, they return a value Control.Monad and friends are very useful.

Elimination Finally some Category Theory.

m a b Pipe a b m r On exhaustion: r

m _ _ Effect m r On exhaustion: r Proxy X () () X m r

Substitution Producers: for or ~> eliminates yield Consumer side: >~ eliminates await

Elimination - Loop Bodies for generator body � for x yield == x for (yield x) f == f x

Companion Libraries Where the features are hiding.

Companion Libraries pipes-parse pipes-safe pipes-group

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.

2. Pipes Safe ReaderT (IORef (Finalizers m)) m r Resource management, exception safety, through a monad transformer on m that allows registering Finalizers.

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

return () :: Effect Talk ()

References Pipes haddocks - Pipes, Pipes.Prelude, Pipes.Tutorial Haskell for All - Gabriel Gonzales’ blog Haskell Pipes Google Group “pipes-“ seach on hackage