Re: [pure-lang-users] Numeric Arguments

[Eddie R. <er...@bm...>]

On Tue, 2008-07-08 at 09:44 +0200, Albert Graef wrote:
> Eddie Rucker wrote:
> > A reasonable manner suggests x = (x mod N) + (x div N) * N
> 
> ... where x div N is integer and abs (x mod N) < abs N I guess, with x
> mod N the same sign as x?

Yes.

> That implicit definition should work with any combination of real-valued
> operands (provided that N is nonzero, of course). Division of a complex
> by a real could be lifted from that, but I'm not sure whether we
> actually want it?

Please don't implement the complex stuff. Implementing mathematics
libraries is kind of like boxing, unless you spend a lot of time in the
ring, you are going to get your jaw jacked. In my *very humble opinion*,
if we want to implement anything, that would be mod and div operators
that obey Scheme's R6RS rules as you alluded to below.

> And we need to decide what to do with division by zero. Machine int and
> bigint division both raise a SIGFPE right now (at least on Linux), which
> is a bit inconvenient. ;-) They could be made undefined like in Q. That
> will complicate and slow down the code for machine int division, though;
> right now this is just a single sdiv instruction. Therefore I'd prefer
> to install a signal handler which maps SIGFPE to a corresponding Pure
> exception; that wouldn't incur runtime costs. In any case rational
> division should follow suit (it returns a floating point infinity right
> now). Opinions?

Hmmm. I really don't know. Playing around with computer mathematics is
one thing. Getting it right for the masses is a *monster*. Maybe bring
it up before other language designers and see what they say.

> Then it probably follows R5RS. AFAICT R6RS specifies div and mod (and
> variations) which work with all real (but not with complex) arguments.

It looks like they ditched quotient, remainder, and modulo for new functions div, div0, mod, mod0, div-and-mod, and div0-and-mod0.

I'm not sure I want to vote for anything right now.

e.r.