Hi all, I’m trying to implement the fast Fourier transform (FFT), using the homogeneous functions described in Sec. 4.2 of *Arrows and Computation* by Ross Paterson: -- FFT implementation -- Note my reversal of Ross' even/odd convention, below. -- I did this, to remain consistent with the explanation, above, which came from a pre-existing work. fft :: RealFloat b => Hom (Complex b) (Complex b) fft = id :&: proc (e, o) -> do e' <- fft -< e o' <- fft >>> twiddle -< o unriffle -< f (e', o') where f (x, y) = (x + y, x - y) twiddle :: RealFloat b => Hom (Complex b) (Complex b) twiddle = id :&: twiddle' 1 twiddle' :: RealFloat b => Int -> Hom (Pair (Complex b)) (Pair (Complex b)) twiddle' n = (id *** (* phi)) :&: (((twiddle' n') *** ((twiddle' n') >>> (arr ((* phi) `prod` (* phi))))) >>> unriffle) where phi = cis (-pi / (fromIntegral (2 ^ n))) n' = n + 1 I’m getting this output, which means that, while my *twiddle* function is working for all tree depths tested, my *fft* function fails for tree depths greater than 3: Tree depth: 0 Testing twiddles...True Testing FFT...True Tree depth: 1 Testing twiddles...True Testing FFT...True Tree depth: 2 Testing twiddles...True Testing FFT...True Tree depth: 3 Testing twiddles...True Testing FFT...True Tree depth: 4 Testing twiddles...True Testing FFT...False Tree depth: 5 Testing twiddles...True Testing FFT...False And I’m wondering if anyone sees the flaw in my code. More here: https://htmlpreview.github.io/?https://github.com/capn-freako/Haskell_Misc/b... https://htmlpreview.github.io/?https://github.com/capn-freako/Haskell_Misc/b... Thanks! -db