Re: [Chicken-users] mathematical oddities

[Peter Bex]

On Thu, Jul 15, 2010 at 08:40:50AM -0400, John Cowan wrote:
> Peter Bex scripsit:
> 
> > Chicken has made a choice to raise an error.  I think that's a
> > respectable decision.  I use Javascript at work quite a bit and
> > the infinities are quite often a source of bugs; you get some error
> > later on when you try to use the infinity, instead of at the point the
> > infinity is produced.  I much prefer to be alerted right away that I'm
> > trying to perform an undefined operation like division by zero.
> 
> The reason to return +0.inf from (/ 3.0 0.0) is that 0.0 is not a
> mathematical zero: rather, it refers to any number r where -DBL_MIN <
> r < DBL_MIN (DBL_MIN is defined in the C header <float.h>).  Dividing by
> exact 0, on the other hand, clearly should throw an exception.

I forgot about that.  Of course, rounding and representation issues make
things even more "interesting".

> I'm not sure what you mean by getting an error when dealing with infinity
> in JavaScript.  Are you confusing infinity with NaN? 

No, but NaN does have many of the same problems (in deferring errors to
later points in time).  I was thinking about my current project at work
where I have to draw graphs on a canvas.  Occasionally I divide something
by some other value and use the result as a location on the canvas.
This causes problems when the result of the division is NaN or Infinity.
Of course this is wrong, but I'd prefer to get an error when I do the
division, and not when I am trying to draw the calculated result (which
is several lines and function calls later).  That would make debugging a
lot easier. Oh well.

> In addition, JavaScript forces you to use inexact arithmetic even
> where exact arithmetic makes more sense; Scheme doesn't.

Indeed.  I guess this is where my reasoning falls on its face with JS,
at least, considering your earlier point about 0.0 not being exactly 0.

Cheers,
Peter
-- 
http://sjamaan.ath.cx
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