Hello haskell-cafe;

I'm fiddling with this blog post about inverting elements of Z/(p), trying to write the inversion function in pointfree style. This led me to try executing statements like

n `mod` 0

which in the ring theoretic sense should be n, at least for integers*. (MathWorld agrees.) But Hugs gives a division by zero error! I'm more of a recreational haskell user and not too familiar with how the Prelude works. But I dug around a bit and saw this in GHC.Real: (link)

>  a `mod` b
>   | b == 0                     = divZeroError

>   | a == minBound && b == (-1) = overflowError

>   | otherwise                  =  a `modInt` b


Is there a reason why n `mod` 0 is undefined in Haskell? Maybe this has already been considered for Haskell' and I'm just unaware. 
I did some digging in the archives and this discussion from 2002 is the most relevant one I could find; it is suggested there that n `mod` 0 should be an error.


Thanks all-
Nathan Bloomfield

*- The mod function is defined in the Integral class, and I'm not even sure how to interpret that. It looks kind of like a Euclidean domain.