[Haskell-cafe] ArrowLoop and streamprocessors

[Paul L]

Forgot to CC the list, please see below.

On Wed, Mar 30, 2011 at 2:29 PM, Mathijs Kwik <bluescreen303 at gmail.com> wrote:

> someBox :: Either A B ~> O
> someBox = handleA ||| handleB

Not sure about this. If you are modeling the input as Either A B, then
you are excluding the possibility of both A and B occur at the same
time. I suggest you change the type to:

someBox :: (Maybe A, Maybe B) ~> O

Based on your later comments, you implied that there could be multiple
B produced from one O. Then I'd suggest the following type:

someBox :: (Maybe A, [B]) ~> O

> otherBox :: O ~> Either C B
>
> Also note that in this CPS style streamprocessing, there's no 1-on-1
> relation between input and output, so on 1 input (O), otherBox might
> produce 2 outputs (2 times C), or 4 outputs (3 times C and 1 time B).

If the number of inputs do not match the number of outputs, I suggest
you change the type to:

otherBox :: O ~> [Either C B]

> To "wire back" B's to someBox, I'm pretty sure I need to use ArrowLoop.
> But (loop :: a (b, d) (c, d) -> a b c) uses tuples, which means the
> processing will only continue when both inputs are available.
> So if I turn someBox into (A, B) ~> O and otherBox into O ~> (C, B),
> the processing will instantly halt, waiting for a B to arrive after
> the A comes in.

You can do something like this, first, split the B out of the ouput:

split :: [Either C B] ~> ([C], [B])

Then the loop back:

loop (someBox >>> otherBox >>> split) :: Maybe A ~> [C]

--
Regards,
Paul Liu