Proposal: Improve the API for TChan, TMVar, and TVar

[Bas van Dijk]

On 26 March 2011 21:30, wren ng thornton <wren at freegeek.org> wrote:
> On 3/26/11 11:43 AM, Antoine Latter wrote:
>>
>> On Sat, Mar 26, 2011 at 6:26 AM, Bas van Dijk<v.dijk.bas at gmail.com>
>>  wrote:
>>>
>>> On 26 March 2011 10:29, wren ng thornton<wren at freegeek.org>  wrote:
>>>>
>>>>    tryReadTChan :: TChan a ->  STM (Maybe a)
>>>
>>> +1 if we also add:
>>> tryReadChan :: Chan a ->  IO (Maybe a)
>>>
>>>>    peekTChan :: TChan a ->  STM a
>>>>    tryPeekTChan :: TChan a ->  STM (Maybe a)
>>>
>>> +1 if we also add:
>>> peekChan :: Chan a ->  IO a
>>> tryPeekChan :: Chan a ->  IO (Maybe a)
>>
>> Here's the last time 'tryReadChan' came up, for reference:
>> http://thread.gmane.org/gmane.comp.lang.haskell.libraries/14596
>>
>> I feel like these sorts of operations are much easier to get right in STM.
>
> Agreed. I'm all for adding Chan versions to base if we can get the
> implementation/semantics right, but since I don't have experience with Chans
> I'm not sure if I'm the best person for that task.

The attached patch adds:

tryReadMVar :: MVar a -> IO (Maybe a)
tryReadChan :: Chan a -> IO (Maybe a)
peekChan :: Chan a -> IO a
tryPeekChan :: Chan a -> IO (Maybe a)

tryReadMVar and tryReadChan were taken from the patch from Mitar.
Thanks Antoine for linking that ticket.

Someone should definitely take a closer look at peekChan and
tryPeekChan and verify if they're correct.

Wren, something else: in the documentation of your new STM operations
you talk about "blocking". I think it's clearer and more consistent
with the rest of STM if you talk about "retrying" instead.

Regards,

Bas
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