import System.Random

data LehmerTree = LehmerTree {nextInt :: Int,
                              leftBranch :: LehmerTree,
                              rightBranch :: LehmerTree}

instance Show LehmerTree where
  show g = "LehmerTree, current root = "++(show $ nextInt g)

mkLehmerTree :: Int->Int->Int->Int->Int->Int->LehmerTree
mkLehmerTree aL aR cL cR m x0 = innerMkTree x0
  where
    mkLeft x = (aL * x + cL) `mod` m
    mkRight x = (aR * x + cR) `mod` m
    innerMkTree x = let l = innerMkTree (mkLeft x)
                        r = innerMkTree (mkRight x)
                    in LehmerTree x l r

mkLehmerTreeFromRandom :: IO LehmerTree
mkLehmerTreeFromRandom = do gen<-getStdGen
                            let a:b:c:d:e:f:_ = randoms gen
                            return $ mkLehmerTree a b c d e f

instance RandomGen LehmerTree where
  next g = (fromIntegral.nextInt $ g, leftBranch g)
  split g = (leftBranch g, rightBranch g)
  genRange _ = (0, 2147483562) -- duplicate of stdRange



test :: IO()
test = do gen<-mkLehmerTreeFromRandom
          print gen
          let (g1,g2) = split gen
          let p = take 10 $ randoms gen :: [Int]
          let p' = take 10 $ randoms g1 :: [Int]
          -- let p'' = take 10 $ randoms g2 :: [Float]
          print p
          print p'
          -- print p''