Proposal: Make gcd total

[Daniel Fischer]

On Saturday 28 May 2011 14:26:45, Ross Paterson wrote:
> On 28 May 2011 11:59, Daniel Fischer wrote:
> > I would like to propose the elimination of the special error case
> > 
> > gcd 0 0 = error "Prelude.gcd: gcd 0 0 is undefined"
> 
> Just deleting that line sounds good.  For documentation, I'd suggest:
> 
>   gcd x y is the non-negative factor of both x and y of which every
>   common factor of x and y is also a factor; for example gcd 4 6 = 2,
>   gcd (-4) 6 = 2, gcd (-4) (-6) = 2, gcd 0 4 = 4, gcd 0 0 = 0.
>   (That is, the common divisor that is "greatest" in the divisibility
>   ordering.)
> 

Thanks, that's pretty nice.

(By the way, non-negative, like the current positive, is not entirely true, 
for bounded signed integer types [with twos' complement representation],
gcd minBound minBound = gcd minBound 0 = minBound < 0,
should that special case be mentioned or should we ignore it like we 
currently do?)