I'm not sure at all why this doesn't compile:
http://lpaste.net/107265
It looks exactly the same as left/right from Pipes.Extras, and it makes
complete sense in my head, but the compiler thinks p is never transformed
into p' in the Pipe p p'.
On Wednesday, July 9, 2014 11:53:27 PM UTC+10, Gabriel Gonzalez wrote:
>
> You're welcome!
>
> On 7/9/14, 1:40 AM, Kyle Van Berendonck wrote:
>
> Thanks, and sorry for delayed reply.
>
> I hadn't thought of doing it like how +++ does it, by just chaining the
> pipes.
>
> On Wednesday, July 9, 2014 3:20:12 AM UTC+10, Gabriel Gonzalez wrote:
>>
>> You can do this using `Pipes.Extras.(+++)`:
>>
>> p1 :: Pipe a d m r
>> p2 :: Pipe b e m r
>> p3 :: Pipe c f m r
>>
>> (p1 +++ p2) +++ p3 :: Pipe (Either (Either a b) c) (Either (Either d
>> e) f) m r
>>
>> Then all you have to do is just stick `Pipes.Prelude.map` upstream of
>> that to convert a `Signal` to a nested `Either`, and then also stick a
>> `Pipes.Prelude.map` downstream of that to unify your handlers. I think it
>> would look like this, but I haven't type-checked this yet:
>>
>> dispatcher :: Mode p p' e c m -> Pipe (Signal e c p) p' m ()
>> dispatcher mode =
>> Pipes.Prelude.map toEither
>> >-> ((handlePacket mode +++ handleEvent mode) +++ handleCommand
>> mode)
>> >-> Pipes.Prelude.map fromEither
>> where
>> toEither s = case s of
>> SigPacket p -> Left (Left p)
>> SigEvent e -> Left (Right e)
>> SigCommand c -> Right c
>>
>> fromEither e = case e of
>> Left (Left p')) -> p'
>> Left (Right p')) -> p'
>> Right p' -> p'
>>
>> That will preserve the individual state of each handler.
>>
>> On 7/8/14, 8:09 AM, Kyle Van Berendonck wrote:
>>
>> I have a sum type which looks like this:
>>
>> data Signal e c p = SigEvent e | SigCommand c | SigPacket p
>>
>>
>> I would like the user to be able to provide functions:
>>
>> type Handler p p' m = Pipe p p' m ()
>>> data Mode p p' e c m = Mode
>>> { handlePacket :: Handler p p' m
>>> , handleEvent :: Handler e p' m
>>> , handleCommand :: Handler c p' m }
>>
>>
>> and have my single input pipe (dispatcher :: Pipe (Signal e c p) p' m
>> ()) fork between the three handlers, while preserving the state of each.
>> ie, one handling commands may use `await` but the next packet could be an
>> event, so it would stay in await until a command arrives. One handler pipe
>> quitting/finishing should result in all quitting.
>>
>> I would not like intermediate containers or forking threads to be part
>> of the solution, since it will be a tight loop.
>>
>> Ideally, I need something like `next` which can be called in the other
>> direction. Ideas?
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