gcd 0 0 = 0

Simon Peyton-Jones simonpj@microsoft.com
Fri, 14 Dec 2001 01:18:56 -0800

|    Probably, the best specification would be
|      gcd n m :: Integer =3D if  n =3D=3D 0 && m =3D=3D 0  then  0
| 			  else
| 			    greatest integer that divides both n and m

Well, thank you all those that have contributed.  My original point
was simply to say

	greatest (positive) integer that divides both n and m

but debate seems to have swirled round whether (gcd 0 0) should
be 0 or an error.  Currently in H98 it's an error; but it is the kind=20
of thing I'm willing to change IF there is a consensus, because it
will only make more programs work.  Is there a consensus that
such a change would be desirable?

If someone could write a sentence or two to explain why gcd 0 0 =3D 0,
(ideally, brief ones I can put in the report by way of explanation),
I think that might help those of us who have not followed the details
of the discussion. =20