[Haskell-cafe] Request for optimizing help.

[Captain Freako]

Does anyone have any advice for optimizing the code, below?
Currently, the profiling results look like this:

COST CENTRE                    MODULE               %time %alloc

runFilter                      Filter                90.9   41.0
convT                          Filter                 9.1   58.6

Thanks for any help!
-db

 11 data FilterState a = FilterState {
 12     as   :: [a] -- transfer function denominator coefficients
 13   , bs   :: [a] -- transfer function numerator coefficients
 14   , taps :: [a] -- current delay tap stored values
 15   } deriving (Show)
 16
 17 type Kernel a = (a, FilterState a) -> (a, FilterState a)
 18
 19 -- FILTER KERNELS
 20 -- Time domain convolution filter (FIR or IIR),
 21 -- expressed in direct form 2
 22 convT :: (Fractional a) => Kernel a
 23 convT (x, s) =
 24     let wk = (x - sum [a * t | (a, t) <- zip (tail $ as s) (taps s)]) /
head (as s)
 25         newTaps = wk : init (taps s)
 26         s' = s {taps = newTaps}
 27         y  = sum [b * w | (b, w) <- zip (bs s) (wk : taps s)]
 28     in (y, s')
 29
 30 -- FILTER APPLICATION
 31 runFilter :: Kernel a -> FilterState a -> [a] -> IO ([a], FilterState a)
 32 runFilter f s0 [] = do
 33     return ([], s0)
 34 runFilter f s0 (x:xs) = do
 35     (y, s') <- return (f (x, s0))
 36     (ys, s) <- runFilter f s' xs
 37     return (y:ys, s)
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