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

[Ryan Ingram]

Never mind, I misread the code, 'zip' and the lazy definition of stream
should add the necessary laziness.

  -- ryan

On Tue, Nov 1, 2011 at 3:36 PM, Ryan Ingram <ryani.spam at gmail.com> wrote:

> 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
>>
>> _______________________________________________
>> Haskell-Cafe mailing list
>> Haskell-Cafe at haskell.org
>> http://www.haskell.org/mailman/listinfo/haskell-cafe
>>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.haskell.org/pipermail/haskell-cafe/attachments/20111101/fc8e5082/attachment.htm>