sign :: Double -> Bool
sign x = (x >= 0)


root :: (Double->Double)->Double->Double->Double->Double
root func left right eps =
    let temp = (left+right)/2
    in
    if (abs $ func $ temp) < eps
        then temp
        else
            if sign (func temp) == sign (func left)
                then root func temp right eps
                else root func left temp eps