Thanks for the answers. These options should work. I don't actually need to
do arithmetic on these values, just construct values that are not
out-of-bounds. Thus efficiency is not a major concern.
On Sat, Mar 27, 2010 at 7:44 PM, Maciej Piechotka
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
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