Hello haskell-cafe; I'm fiddling with thishttp://cdsmith.wordpress.com/2009/07/20/calculating-multiplicative-inverses-...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. http://mathworld.wolfram.com/Congruence.html) 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 inGHC.Real: ( linkhttp://www.haskell.org/ghc/docs/latest/html/libraries/base/src/GHC-Real.html... )
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 http://markmail.org/message/5dmehw4lhu56x4zw#query:haskell%20%22%60mod%60%20... http://markmail.org/message/5dmehw4lhu56x4zw 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.