Nil question

ruby-talk
1

Lähettäjä: E S <eero.saynatkari@kolumbus.fi>
Aihe: Re: nil question

> Lähettäjä: "David A. Black" <dblack@wobblini.net>
> Aihe: Re: nil question
>
> Hi --
>
>
> > "David A. Black" <dblack@wobblini.net> writes:
> >
> >> Hi --
> >>
> >>
> >>> "William James" <w_a_x_man@yahoo.com> writes:
> >>>
> >>>> Sam Roberts wrote
> >>>>> In ruby, zero and empty strings are true
> >>>>
> >>>> Since 0 is true, you should be able to do this in Ruby:
> >>>>
> >>>> puts "yes" if -5 < x < 9
> >>>>
> >>>> The phrase '-5 < x' should yield the value of x instead of true.
> >>>> That's the way it actually works in the Icon programming language.
> >>>> But we have to use the klunky
> >>>>
> >>>> puts "yes" if -5 < x and x < 9
> >>>>
> >>>
> >>> Erm, say, x is -16:
> >>>
> >>> (-5 < x) < 9
> >>> (-5 < -16) < 9
> >>> -5 < 9
> >>> -5
> >>>
> >>> -5 is true, probably not what you want.
> >>
> >> But -5 < -16 is not true, so it wouldn't get that far. (I assume
> >> William means it should return x if the expression is true, false
> >> otherwise.)
> >
> > So false is bigger than 9? Math books will need to be rewritten. :slight_smile:
>
> I assume the expression would short-circuit once one of the
> sub-expressions returned false, since
>
> x < y < z
>
> cannot be true unless x < y. So there would never be a false < z
> comparison.

So...

class Numeric
  alias :old_lt :<
  alias :old_gt :<

  def <(val)
    val if self.old_lt val
    false
  end

  def >(val)
    val if self.old_gt val
    false
  end
end

>> x = 5
>> puts 4 < x < 6
=> 5
>> puts 6 < x < 7
=> false

?

Stupid webmail. Fixnums and Numerics probably just use <=> and
<, > from Comparable instead, so this'd require changes to the
core there. Also:

class FalseClass
  def <(val)
    false
  end
end

# And this...

x = 5
puts 4 < x < 6

# ...should of course return:
=> 6 # or 'true' in a conditional.

> David

E

···

> On Mon, 31 Jan 2005, Christian Neukirchen wrote:
> >> On Sun, 30 Jan 2005, Christian Neukirchen wrote: