On 04/26/2010 12:50 PM, haskell@kudling.de wrote:
Hi list,
how would you describe Ada's ranges in Haskell's typesystem?
Hi Lenny, can non-constant expressions be given as arguments to 'range'? If not, then what about a opaque wrapper type? {-# LANGUAGE GeneralizedNewtypeDeriving #-} module Range1 (Range1, fromRange1, mkBounded, mkRange1) where newtype Range1 = Range1 { fromRange1 :: Integer } deriving (Eq, Num, Ord, Show) instance Bounded Range1 where minBound = Range1 $ -5 maxBound = Range1 $ 10 mkBounded :: (Bounded a, Ord a) => (b -> a) -> b -> Maybe a mkBounded f x = case f x of y | minBound <= y && y <= maxBound -> Just y | otherwise -> Nothing mkRange1 :: Integer -> Maybe Range1 mkRange1 = mkBounded Range1 -- Steffen