Sorry I really should've tested my code before I hit send.
instance FromJSON CUid where
parseJSON (Number n) = do
case floatingOrInteger n of
Right i | inrange i -> return . CUid . fromIntegral $ i
_ -> mempty
where
inrange :: Integer -> Bool
inrange i = i >= fromIntegral (minBound @Word32) &&
i <= fromIntegral (maxBound @Word32)
parseJSON _ = mempty
On Thu, Aug 9, 2018 at 1:06 PM, David McBride
You have to worry about json having a floating point number or an integer that is too large to be represented in a Word32, although you could also just let it overflow if you don't care too much. There's probably an easier way to do this, but this is what I came up with.
instance FromJSON CUid where parseJSON (Number n) = do
case floatingOrInteger n of Right i | inrange i -> return . CUid . fromIntegral $ i
-- not an integer, or not in range _ -> mempty
where inrange :: Integer -> Bool inrange i = fromIntegral i >= (minBound @Word32) && fromIntegral i <= (maxBound @Word32)
-- not a number parseJSON _ = mempty
On Thu, Aug 9, 2018 at 11:37 AM, PICCA Frederic-Emmanuel < frederic-emmanuel.picca@synchrotron-soleil.fr> wrote:
Hello, I try to write the instance for the CUid[1] type But I do not know what to do.
instance FromJSON CUid where parseJSON = ... {-# INLINE parseJSON #-}
Thansk for your help
[1] https://hackage.haskell.org/package/base-4.11.1.0/docs/Syste m-Posix-Types.html#t:CUid _______________________________________________ Beginners mailing list Beginners@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners