[Haskell-beginners] merge two handles

[David McBride]

It probably has to do more with parenthesis than anything:

forever $ atomically $ readTchan chan >>= print
forever $ (atomically $ readTchan chan) >>= print

That might work.  Once you get the types to line up, that should work.

On Tue, Jun 14, 2011 at 11:26 AM, Manfred Lotz <manfred.lotz at arcor.de> wrote:
> On Mon, 13 Jun 2011 15:14:26 -0500
> Antoine Latter <aslatter at gmail.com> wrote:
>
>> On Mon, Jun 13, 2011 at 1:14 PM, Manfred Lotz <manfred.lotz at arcor.de>
>> wrote:
>> > On Mon, 13 Jun 2011 12:51:02 -0500
>> > Antoine Latter <aslatter at gmail.com> wrote:
>> >
>> >> On Mon, Jun 13, 2011 at 12:35 PM, Manfred Lotz
>> >> <manfred.lotz at arcor.de> wrote:
>> >> > Hi all,
>> >> > I have two handles where I get stdout resp. stderr from a command
>> >> > output.
>> >> >
>> >> >
>> >> > Is it possible to merge those two handles so that I get a new
>> >> > input handle in a way that data can be read from the new handle
>> >> > whenever it is available from either of the two original handles?
>> >> >
>> >> >
>> >>
>> >> Does what you're doing strictly need to be a handle?
>> >>
>> >> One thing you could try is is using an IO Channel:
>> >> http://hackage.haskell.org/packages/archive/base/latest/doc/html/Control-Concurrent-Chan.html
>> >>
>> >
>> > Hmm, not quite sure. I was asking about handles because I use:
>> >
>> > (_ ,Just hout ,Just herr ,p) <- createProcess (proc cmd parms) {
>> >    std_out = CreatePipe,
>> >    std_err = CreatePipe
>> >  }
>> >
>> >
>> > which gives me handles to deal with.
>> >
>>
>> You could create the pipe yourself, and then call 'createProcess' with
>> 'UseHandle' instead, passing the same handle to both std_out and
>> std_error.
>>
>> On a unix-y system you can do this with the functions in
>> System.Posix.IO.
>>
>> I'm not sure what you would do on windows. This might be a good
>
> I'm on a Linux system. Don't use Windows.
>
> Thanks for pointing to this. In the meantime I found something similar
> in the online book "Real World Haskell". So I have something to try out.
>
>
>
>
> --
> Manfred
>
>
>
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