[ruby-talk:13465] Re: A subtle Hash bug

On Fri, 30 Mar 2001, Christoph Rippel wrote:
> > Is there any good reason why Float's "Infinity" value is equal to itself?
> > And then, is there any good reason why it shouldn't be changed?
> Well,
> the outcome of floating point division of 1 by +/-0.0 is either 
> Infinity or -Infinity and that they are different that just a 
> reflection of standard C double behavior. Not you can use 
> +/- Infinity as regular input and gets something sensible like
> p Math.atan(1/-1.0)  # => -0.7853981634  a.k.a -Pi/4
> p Math.atan(1/1.0)   # => 0.7853981634
> so +/-Infinities have to be different. The 

I'm not proposing that +Infinity should be indistinguishable from
-Infinity. I'm asking why is +Infinity == +Infinity and -Infinity ==
-Infinity.

> hack is hardware independent and should work on all platforms. 
> The exception raising behavior of zero-division and comparison
> is type specific on the method receiver end
>  2**29 <=> 1/0.0  # => -1 since  2**29 is a Fixnum   
>  2**33 <=> 1/0.0  # FloatDomainError: Infinity since 2**33 is Bignum

this should return -1 since although +Infinity is not a precise number, it
is greater than all other finite values and -Infinity. (it is however
noncomparable to itself and to NaN)

>  1/ 0             # a ZeroDivisionError is raised for any Integer type

This is ok, because the Integer domain has no equivalent of Infinities and
NaNs.

> I actually have a Ruby hack of logical +/- Infinity's constants.
> The semantics is closer to +/- nil and but you can perform limited
> Arithmetic on them - I made them instances of +/- Infinity Classes
> sub-typed from Numeric but this is not really necessary. (the are
> necessarily smaller/bigger then floats infinities).

May I see that? Btw, what are +nil and -nil ???

> methods input of any numeric object (except for Rational, which
> is an eager beaver and tries to process input it does not 
> understand instead of calling coerce).

Do you think Rational should be fixed to act, ehm, more rationally?

matju