Proposal: Add tryReadChan to Chan

Antoine Latter aslatter at
Wed Dec 1 00:55:34 CET 2010

All of this really feels like what STM is good at. It might help if you
explained why TChans are not well suited to your task.
On Nov 26, 2010 6:51 PM, "Mitar" <mmitar at> wrote:
> Hi!
> Now that isEmptyChan is deprecated (#4154) it would be useful to add
> tryReadChan. It seems it is possible to define it so that it does not
> block like isEmptyChan. This is because semantics is a bit different:
> tryReadChan is allowed to return Nothing also when Chan is non-empty,
> but it would block. Contrary, isEmptyChan is expected that it would
> return False only if Chan is really empty.
> I have defined also two new MVar functions which helped me
> implementing tryReadChan: tryReadMVar and tryModifyMVar. Probably it
> would be useful to make them public.
> Please comment. I propose three weeks for discussion.
> I have also opened a ticket:
> and attached a ptach there with working implementation. It would be
> useful to run it against some tests.
> (I am sorry that patch is not in darcs format.)
> Mitar
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