Hi all! I'm new to Haskell... absolutely new. I need some practice, but little problem seems to me like unresolvable... Is there some tutorial of "Exercise, set of resolutions" pairs type? My english is very bat, so there is it in a picture: Exercise 1: hello world Hint: use 'putStrLn' Resolution 1.1 Resolution 1.2 Exercise 2: write functions 'max_num', 'solve_quad_equation', 'reverse_ary' Hint: (Explanation of some technics) Res... Excercise 3: Use do-notation to reverse word in a line read from stdin Hint: Use Exercise 2... (Explain how 'do' works and what to do in common error sitations) So, in a word: I need a tutorial for dummies Now, my current problem is: my program for solving quadratic equation won't compile... import System solve_qe :: Maybe (Double, Double, Double) -> Maybe (Double, Double) solve_qe Nothing = Nothing solve_qe (a, b, c) | d >= 0 = Just ((-b + (sqrt d)) / (2 * a), (-b - (sqrt d)) / (2 * a)) | otherwise = Nothing where d = b^2 - 4*a*c evalArgs :: [String] -> Maybe (Double, Double, Double) evalArgs (a:b:c:[]) = (read a, read b, read c) evalArgs _ = Nothing main = do args <- getArgs print (solve_qe (evalArgs args))