Behaviour of div & mod with negative arguments?

[Simon Marlow]

> Does Haskell specify how div and mod should behave when
> given one or both arguments negative?
>=20
> Eg, in hugs we get:
>=20
> div   1    3  =3D 0
> div (-1)   3  =3D -1
> div   1  (-3) =3D -1
> div (-1) (-3) =3D 0
>=20
> and so on.

We usually describe div as the version of division that "truncates
towards negative infinity".  What this actually means is that when there
are two solutions to

	a `divMod` b =3D (d,m) =20
      such that  d*b + m =3D=3D a=20
      and        abs m < b

div picks the one where d is the closest to minus infinity, and quot
picks the one where d is closer to zero.

  eg.  (-1) `divMod` 3  =3D (-1, 2)   or  (0, -1)

divMod gives you (-1,2), whereas quotRem gives you (0,-1).

Hope this helps.

Cheers,
	SImon