Streaming.Eversion

Most pull-to-push transformations in this module require functions that are polymorphic over a monad transformer.

Because of this, some of the type signatures look scary, but actually many (suitably polymorphic) operations on Streams will unify with them.

To get "interruptible" operations that can exit early with an error, put a ExceptT transformer just below the polymorphic monad transformer. In practice, that means lifting functions like throwE and hoistEither a number of times.

Inspired by http://pchiusano.blogspot.com.es/2011/12/programmatic-translation-to-iteratees.html

Stream folds

evert

Arguments

:: (forall m r. Monad m => Stream (Of a) m r -> m (Of x r))

-> Fold a x

evertM

Arguments

:: Monad m

=> (forall t r. (MonadTrans t, Monad (t m)) => Stream (Of a) (t m) r -> t m (Of x r))

-> FoldM m a x

Like evert, but gives the stream-folding function access to a base monad.

>>> :{
    let consume stream = lift (putStrLn "x") >> S.effects stream
    in  L.foldM (evertM_ consume) ["a","b","c"]
    :}
x

Note however that control operations can't be lifted through the transformer.

evertM_

Arguments

:: Monad m

=> (forall t r. (MonadTrans t, Monad (t m)) => Stream (Of a) (t m) r -> t m r)

-> FoldM m a ()

evertMIO

Arguments

:: MonadIO m

=> (forall t r. (MonadTrans t, MonadIO (t m)) => Stream (Of a) (t m) r -> t m (Of x r))

-> FoldM m a x

Like evertM, but gives the stream-consuming function the ability to use liftIO.

>>> L.foldM (evertMIO_ S.print) ["a","b","c"]
"a"
"b"
"c"

evertMIO_

Arguments

:: MonadIO m

=> (forall t r. (MonadTrans t, MonadIO (t m)) => Stream (Of a) (t m) r -> t m r)

-> FoldM m a ()

Stream transformations

transvert

Arguments

:: (forall m r. Monad m => Stream (Of a) m r -> Stream (Of b) m r)

-> Fold b x

-> Fold a x

transvertM

Arguments

:: Monad m

=> (forall t r. (MonadTrans t, Monad (t m)) => Stream (Of a) (t m) r -> Stream (Of b) (t m) r)

-> FoldM m b x

-> FoldM m a x

transvertMIO

Arguments

:: MonadIO m

=> (forall t r. (MonadTrans t, MonadIO (t m)) => Stream (Of a) (t m) r -> Stream (Of b) (t m) r)

-> FoldM m b x

-> FoldM m a x

Internals

generalEvertM

Arguments

:: Monad m

=> (forall r. Stream (Of a) (Stream ((->) (Feed a)) m) r -> Stream ((->) (Feed a)) m (Of b r))

-> FoldM m a b

generalTransvertM

Arguments

:: Monad m

=> (forall r. Stream (Of a) (Stream ((->) (Feed a)) m) r -> Stream (Of b) (Stream ((->) (Feed a)) m) r)

-> FoldM m b x

-> FoldM m a x