pipes-cliff - interact with subprocesses using Pipes

[Omari Norman]

Hi all,

I have created a library, pipes-cliff, for interacting with subprocesses using Pipes.

http://hackage.haskell.org/package/pipes-cliff

It aims to be simple and straightforward.  It's not as powerful as process-streaming--for instance you cannot combine standard output and standard error into the same stream (at least, not without doing the work yourself.)  It doesn't do ByteString to Text conversions.  But the API is (hopefully) easier to understand and works for the simple use cases that I need.

See also this previous thread for discussions of the various issues involved with streaming to and from subprocesses.

https://groups.google.com/forum/#!msg/haskell-pipes/JFfyquj5HAg/Lxz7p50JOh4J

Feedback and bug reports welcome.  Thanks.  --Omari

[Gabriel Gonzalez]

Awesome!  Thanks for doing this! :)

I was browsing the API and I just wanted to mention that you can simplify the constraints a little bit.  You have a couple of places where the constraint is:

    (MonadIO m, MonadSafe m) => ...

... and you can simplify that to just `MonadSafe m` because `MonadIO` is a super-class of `MonadSafe` in the latest versions of `pipes-safe`.

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[Daniel Díaz]

One doubt: when using pipeOutputError, is it possible to take the output and error producers and consume them concurrently in separate threads, for example using the Concurrently applicative from Control.Concurrent.Async?

[Omari Norman]

On Fri, Mar 20, 2015 at 8:36 PM, Daniel Díaz <diaz.c...@gmail.com> wrote:

One doubt: when using pipeOutputError, is it possible to take the output and error producers and consume them concurrently in separate threads, for example using the Concurrently applicative from Control.Concurrent.Async?

Certainly you can consume them concurrently--in fact,  you would need to, or else the subprocess might block when its standard error or standard output fills up.  Each Producer returned by 'pipeOutputError' has an independent connection to the respective subprocess 'Handle'; concurrent threads will pull data from the subprocess and each 'Producer' will 'yield' its respective 'ByteString's.  You do, however, have to make sure that the 'Consumer' that you hook to the 'Producer' for stdout (or the 'fold' you want to run, or however you want to do it) runs concurrently with the ultimate 'Effect' that pulls from standard error.  There is a 'conveyor' function that makes it easy to run an 'Effect' in a background thread.

I will add an example to Pipes.Cliff.Examples showing how to pull from standard output and standard error.