[Haskell-cafe] How to implement digital filters using Arrows

[Ryan Ingram]

Try

swap p = (snd p, fst p)

or, equivalently

swap ~(x,y) = (y,x)

  -- ryan

On Tue, Nov 1, 2011 at 1:30 PM, Captain Freako <capn.freako at gmail.com>wrote:

> Hi John,
>
> I'm trying to use the GHCI debugger on this code:
>
>  20 instance ArrowLoop SF where
>  21     loop (SF f) = SF $ \as ->
>  22         let (bs, cs) = unzip (f (zip as (stream cs))) in bs
>  23       where stream ~(x:xs) = x : stream xs
>  24
>  25 swap :: (a,b) -> (b,a)
>  26 swap (x,y) = (y,x)
>
> in order to watch the recursion of the `loop' function unfold.
> However, when I single step through the code, I never stop on line 22
> (where I could, presumably, peek in at `bs' and `cs', in order to see
> them develop):
>
> *SF> :break swap
> Breakpoint 1 activated at SF.hs:26:1-18
> *SF> runSF (loop (arr swap)) [1,2,3]
> Stopped at SF.hs:26:1-18
> _result :: (b, a) = _
> [SF.hs:26:1-18] *SF> :step
> Stopped at SF.hs:26:14-18
> _result :: (b, a) = _
> x :: a = _
> y :: b = _
> [SF.hs:26:14-18] *SF> :
> [1Stopped at SF.hs:23:34-42
> _result :: [a] = _
> xs :: [a] = _
> [SF.hs:23:34-42] *SF> :
> Stopped at SF.hs:23:13-42
> _result :: [a] = _
> [SF.hs:23:13-42] *SF> :
> Stopped at SF.hs:23:30-42
> _result :: [a] = _
> x :: a = _
> xs :: [a] = _
> [SF.hs:23:30-42] *SF> :
> (Pattern repeats.)
>
> Do you have any advice?
>
> Thanks,
> -db
>
>
>
> On Mon, Oct 31, 2011 at 3:19 PM, John Lask <jvlask at hotmail.com> wrote:
> > On 1/11/2011 1:35 AM, Captain Freako wrote:
> >
> > you need to study ArrowLoop and understand that. In the code
>
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