-- ok, something in deriving NFData using Generics in a type that has a Vector in it.

{-# LANGUAGE DeriveGeneric #-}

import Control.DeepSeq

import System.IO

import GHC.Generics (Generic)

import qualified Data.Vector as V

import qualified Data.ByteString.Lazy.Char8 as BL

scanl' :: NFData a => (a -> b -> a) -> a -> [b] -> [a]

scanl' f q ls =  q : (case ls of

                        []   -> []

                        x:xs -> let q' = f q x

                                in q' `deepseq` scanl' f q' xs)

-- this runs without blowing up

-- main = print $ last $ scanl' (+) (0::Int) [0..]

data Simple = Simple (V.Vector Double)

            deriving (Show, Generic)

instance NFData Simple

--this blows up

main = do

   let initial = Simple $ V.fromList (take 100 $ repeat 0)

       sumvs (Simple a) (Simple b) = Simple $ V.zipWith (+) a b

   print $ last $ scanl' sumvs initial $ repeat $ initial