SegTree minimum .hs

data SegTree a b = Empty |
               SegTree { subtL :: SegTree a b
                       , segL :: a
                       , segR :: a
                       , valOnSeg :: b
                       , subtR :: SegTree a b
                       } deriving Show

intINF = maxBound::Int

getVal :: SegTree a Int -> Int
getVal Empty = intINF
getVal tree = valOnSeg tree

buildSegTree :: Int -> Int -> UArray Int Int -> SegTree Int Int
buildSegTree l r arr
  | l+1==r = SegTree Empty l r (arr!l) Empty
  | otherwise = SegTree left l r (min (getVal left) (getVal right)) right
    where mid = (l + r) `div` 2
          left = buildSegTree l mid arr
          right = buildSegTree mid r arr

getMin :: Int -> Int -> SegTree Int Int -> Int
getMin l r Empty = intINF
getMin l r (SegTree subtl tl tr mn subtr)
  | tl >= r || tr <= l = intINF
  | l <= tl && tr <= r = mn
  | otherwise = min (getMin l r subtl) (getMin l r subtr)
    where mid = (tl+tr) `div` 2