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
fromEithere = 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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