On 21/06/2012, at 9:11 PM, Rouan van Dalen wrote:
I was hoping to have some functions like:
safeSucc :: (Enum a) => a -> Maybe a
Types that are instances of Enum don't necessarily have bounds. It always struck me as odd that Enum doesn't extend Ord. There's a reason given for not having Bounded extend Ord, which doesn't really apply to a class having fromEnum :: a -> Int. Testing whether an enum bound is at a limit is thus a bit tricky. isMaxBound, isMinBound :: (Enum t, Bounded t) => t -> Bool isMaxBound x = fromEnum x == fromEnum (maxBound `asTypeOf` x) isMinBound x = fromEnum x == fromEnum (minBound `asTypeOf` x) safeSucc, safePred :: (Enum t, Bounded t) => t -> Maybe t safeSucc x = if isMaxBound x then Nothing else Just (succ x) safePred x = if isMinBound x then Nothing else Just (pred x)