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

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 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 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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