[Haskell-cafe] Trying to write 'safeFromInteger'
ekmett at gmail.com
Wed Apr 8 08:09:55 EDT 2009
Of course your safeFromInteger isn't really safe, what about the minBound?
On Tue, Apr 7, 2009 at 5:27 PM, Kannan Goundan <kannan at cakoose.com> wrote:
> Here's my code (in file "Test.hs")
> safeFromInteger :: (Num a, Integral a, Bounded a) => Integer -> Maybe a
> safeFromInteger i =
> if i > (toInteger maxBound)
> then Nothing
> else Just (fromInteger i)
> Here's the error from GHCi 6.10.1:
> Ambiguous type variable `a' in the constraints:
> `Bounded a' arising from a use of `maxBound' at Test.hs:3:19-26
> `Integral a' arising from a use of `toInteger' at Test.hs:3:9-26
> Probable fix: add a type signature that fixes these type variable(s)
> It's almost like GHC thinks that the type variable "a" can't be part of the
> "Bounded" lass and the "Integeral" class.
> I plan to use "safeFromInteger" for converting from Word8, Word16, Word32,
> Haskell-Cafe mailing list
> Haskell-Cafe at haskell.org
-------------- next part --------------
An HTML attachment was scrubbed...
More information about the Haskell-Cafe