[Haskell-cafe] Confused by ghci output

[Claude Heiland-Allen]

Hi Clark,

ghci is defaulting to Integer
modexp2 forces Int
Int overflows with 3^40

On 31/05/12 17:35, Clark Gaebel wrote:
> *X>  3^40 `mod` 3 == modexp2 3 40 3
> False

*X> fromInteger (3^40 `mod` 3) == modexp2 3 40 3
True

> *X>  modexp2 3 40 3
> 0
> *X>  3^40 `mod` 3
> 0

*X> 3^40 `mod` 3 ::Int
2

> I'm confused. Last I checked, 0 == 0.

Int overflow is ugly!

*X> 3^40
12157665459056928801
*X> maxBound :: Int
9223372036854775807


Claude

>
> Using GHC 7.4.1, and the file x.hs (which has been loaded in ghci) can be
> found here: http://hpaste.org/69342
>
> I noticed this after prop_sanemodexp was failing.
>
> Any help would be appreciated,
>    - Clark
>
>
>
>
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