[Haskell-cafe] Code critique request

[Michael Litchard]

I've got this fizzbuzz project I am using for a blog series, among other
things. In this version, the fizzbuzz function is fed from a Fibonacci
generator. I'm particularly concerned with the efficiency of the Fibonacci
generator, but all scrutiny is welcomed.

I'll included a link to the entire project, but below are the parts I think
would be sufficient to spot trouble with how I am generating Fibonacci
numbers.

-- Driver function performs following-- (1) checks that input is
proper-- (2) creates integer list for fibonacci generator-- (3)
calculates first x in fibonnaci sequence-- (4) generates fizzbuzz
output using (3)

fizzBuzzFib :: [Text] -> Either FizzError [Text]
fizzBuzzFib str =
mapM fizzbuzz          =<<
mapM fibb              =<< -- Possible problem here(\x -> Right [1 .. x]) =<<
convertToPInt          =<<
mustHaveOne str

fibb :: Integer -> Either FizzError Integer
fibb n = Right $ snd . foldl' fib' (1, 0) . map (toEnum .
fromIntegral) $ unfoldl divs n
  where
    unfoldl f x =
      case f x of
        Nothing     -> []
        Just (u, v) -> unfoldl f v ++ [u]

    divs 0 = Nothing
    divs k = Just (uncurry (flip (,)) (k `divMod` 2))

    fib' (f, g) p
      | p = (f*(f+c*g), f^c + g^c)
      | otherwise = (f^c+g^c, g*(c*f-g))
      where
        c :: Integer -- See codebase for reasons
        c = 2

The whole project, for your critiquing
eye:https://github.com/mlitchard/swiftfizz
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.haskell.org/pipermail/haskell-cafe/attachments/20160506/1611c828/attachment.html>