.lhs

> alphas :: String -> String
> alphas xs = filter (isAlpha) xs 

> propAlphasCorrect :: String -> Bool
> propAlphasCorrect xs = isCorrect (alphas xs)
>     where
>         isCorrect ys = all (isAlpha) ys


> uppers :: String -> String
> uppers xs = map toUpper xs

> propUppersCorrect :: String -> Bool
> propUppersCorrect xs = isCorrect (uppers xs)
>     where
>         isCorrect ys = all (isUpper) ys