[Haskell-cafe] Trying to write 'safeFromInteger'

Henning Thielemann lemming at henning-thielemann.de
Fri Apr 10 18:54:12 EDT 2009

On Wed, 8 Apr 2009, Neil Mitchell wrote:

> That seems a really weird way to write it! Who decided all auxiliary
> functions should be called go? (I think I'm blaming dons) - why not:
> sffi :: (Integral a,Num a) => Integer -> Maybe a
> sffi n | toInteger n2 == n = Just n2
>        | otherwise = Nothing
>     where n2 = fromInteger n

I think it is a bug, that 'fromInteger' is defined for numbers outside the 
range of the target type. Why is it necessary to have, say
   fromInteger 1000 == (232 :: Word8)

I would not rely on this behaviour and safeFromInteger should also work, 
when the fromInteger method yields undefined for some Integer input.

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