Haskell Riemann Sums

riemann.hs

data RiemannType = LeftSum | RightSum | MidSum
riemann :: RiemannType -> (Float -> Float) -> Float -> Float -> Float -> Float
riemann rt f a b n = dx * foldr (\l -> \r -> (f $ a + (l * dx)) + r) 0 range
    where
        range = case rt of
            LeftSum -> [0..n-1]
            RightSum -> [1..n]
            MidSum -> [0.5..n-0.5]
        dx = (b-a)/n