plp/haskell/haskell7.hs

--Define the Bilist type
data Bilist a = Bilist [a] [a] deriving (Show, Eq)

bilist_ref (Bilist l r) pos = (l !! pos, r !! pos)

--Define oddeven

oddeven :: [a] -> Bilist a
oddeven l = oddevenh l [] []

oddevenh :: [a] -> [a] -> [a] -> Bilist a
oddevenh [] ev od = Bilist ev od
oddevenh (x:xs) ev od = oddevenh xs od (ev++[x])

--Define the inverse of oddeven

inv_oddeven :: Bilist a -> [a]
inv_oddeven (Bilist [] []) = []
inv_oddeven (Bilist (l:ls) (r:rs)) = [l] ++ [r] ++ (inv_oddeven (Bilist ls rs))

inv_oddeven2 :: Bilist a -> [a]
inv_oddeven2 (Bilist l r) = foldl (++) [] $ map (\(x,y) -> [x,y]) $ zip l r

bilist_max (Bilist (l:ls) (r:rs)) = bilist_maxh (Bilist ls rs) 2 (l+r) 1

bilist_maxh (Bilist (l:ls) (r:rs)) pos curmax maxpos |
        l+r > curmax = bilist_maxh (Bilist ls rs) (pos+1) (l+r) pos
bilist_maxh (Bilist (l:ls) (r:rs)) pos curmax maxpos =
        bilist_maxh (Bilist ls rs) (pos+1) curmax maxpos
bilist_maxh (Bilist [] []) pos curmax maxpos = maxpos