Re: [Haskell-cafe] Trying to write 'safeFromInteger'

Of course your safeFromInteger isn't really safe, what about the minBound? =) On Tue, Apr 7, 2009 at 5:27 PM, Kannan Goundan 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:

Test.hs:3:19: 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, etc.

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