Re: generic * and 0

[Mikael Djurfeldt]

2006/12/4, Kevin Ryde <address@hidden>:
> While nosing around nearby stuff I noticed
>
>         (* 0 1.0)  => 0
>         (* 0 1+1i) => 0
> but
>         (* 1.0  0) => 0.0
>         (* 1+1i 0) => 0.0
>
> which seems a bit inconsistent.

Indeed.

>  R5RS "Exactness" reads like either
> exact or inexact is permitted, but I imagine it ought to be the same
> whichever way around you write the args.  I think I'll change the
> latter two to exact 0.

Good idea.  Because of paragraph 6.2.2, a program cannot expect to get
the result 0.0, and it seems like a strength of the implementation to
provide the additional piece of information that the result is indeed
*exactly* 0.

An added bonus is that it doesn't break the idea to have a common
abstract zero for the * operator.  (Not entirely sure that the common
zero is a good idea, but I tend to think so.)