[Haskell-cafe] ANNOUNCE: pipes-core 0.0.1

Paolo Capriotti p.capriotti at gmail.com
Sat Mar 10 11:16:31 CET 2012

On Sat, Mar 10, 2012 at 4:21 AM, Mario Blažević <blamario at acanac.net> wrote:
>    I like your design, it seems to strike a good balance between elegance
> and practicality. The only thing missing for the latter is a deeper support
> for chunking. Of course, that would probably destroy some of the elegance
> [1]. I don't think that problem has been solved in any of the
> enumerator/iteratee/pipe/wire/conduit libraries so far.

Chunking is supported but not by primitive constructs. The way you
implement chunked streams is to simply use some form of "container"
representing a chunk as your input/output type.

Of course, that means that the abstraction is now operating at the
level of chunks instead of elements, which may be inconvenient, but I
doubt that there exists a way to "lift" element operations to chunks
in an efficient and general way.

Another issue is how to deal with unconsumed input. For that, there is
a ChunkPipe type (in pipes-extra) with a specialized monad instance
that threads unconsumed input along. You can see an example of
ChunkPipe in action in this prototype http server by Jeremy Shaw:
http://src.seereason.com/pipes-http-2/pipes-http-2/. Note that this is
based on a old version of pipes-core, however.

>    Did you consider adding some stream-splitting and merging pipes, like
> those in the SCC package [2] or those described in the last Monad.Reader
> issue [3]? Your arrow-like combinators seem well thought out, but they
> don't go very far.

I'm not sure why you say that they don't go very far. I looked at
Splitter and Join in Monad.Reader 19, and they seem equivalent to
'splitP' and 'joinP' in pipes-core.

There shouldn't be any problem implementing all the other combinators
there in terms of monoidal primitives (e.g. 'not' is just 'swap').

There is also a 'zip' combinator in pipes-extra, that synchronizes two
Producers on their respective outputs.

Can you elaborate on use cases that seem to be missing?


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