Nil question

ruby-talk
1

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

?

David

E

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