After a looking a little more, there seem to be other problems (including errors in my proposed solution). I don't know where the code for quotRem is, but it is also buggy. For instance,

Prelude> 9 `quotRem` (-5) (-1,4)

(The correct answer is (-1,-4).) I'm frankly astonished: has noone used these functions with negative arguments before?

GHC's answer looks right to me, since according to the report: (x `quot` y)*y + (x `rem` y) == x so (-1 * -5) + 4 == 9 but if 9 `rem` (-5) should be -4, then (-1 * -5) + -4 = 1

I'm shocked that non of the three Haskell implementations had a test suite that caught this problem.

Take a look at fptools/testsuite/tests/ghc-regress/numeric/should_run/arith0011.hs. There may be one or two wrong answers lurking in there, but that's a lot of results to check by hand! Cheers, Simon