On Fri, 2010-03-26 at 14:23 -0400, Ashish Agarwal wrote:
Is there an alternative implementation of the types Word8, Word16, etc. that disallow overflow? For example, currently:
Prelude Word> (fromInteger 256) :: Word8 0
I'd like a type whose constructors disallow this.
safeConvert :: (Integral a, Integral b) :: a -> Maybe b safeConvert x | fromIntegral y == x = Just $! y | otherwise = Nothing where y = fromIntegral x You can write: newtype Safe a = Safe a deriving Eq instance Show a => Show (Safe a) where show (Safe x) = show x instance Integral a => Num (Safe a) where (Safe x) + (Safe y) = Safe $! x + y (Safe x) * (Safe y) = Safe $! x * y (Safe x) - (Safe y) = Safe $! x - y negate (Safe y) = Safe $! negate y abs (Safe y) = Safe $! abs y signum (Safe y) = Safe $! signum y fromInteger x = Safe $! fromMaybe (error "overflow") (safeConvert x) ... if you want Regards