gistfile1.hs

fft :: [[Integer]] -> [Integer] -> Integer -> Integer -> Integer -> Integer
fft as rho m mM sig pc = ... cooleyTukey bs (rhoMult m mM) (mM `div` mM) ...
    where Ibs = zipWith (badMult m mM sig pc) pr as
          pr = powersOfRho (m * 2) rho m mM sig pc

data Constants = C { mM :: Integer, sig :: Integer, pc :: Integer}

fft :: [[Integer]] -> [Integer] -> Integer -> Integer -> Integer -> Integer
fft as rho m mM sig pc = runReader fft' (Constants mM sig pc)

fft' = do
    pr <- powersOfRho
    uibd <- zipWithM badMult pr as
    return (cooleyTukey ...)

badMult :: Reader Integer
badMult = do
    m' <- asks m
    <ask for any more values you need to return>
    ...
    let x = <result of computation that used to be badMult>
    return x
    
powersOfRho :: Reader [Integer]
powersOfRho = do
    m' <- asks m
    rho' <- asks rho
    ...
    let x = <computation that used to be in powersOfRho>
    return x