From: Gunnar <gunnar.larsson2@...>
Date: 2005-05-04T02:29:45+09:00
Subject: Re: Pickaxe page 342, Ranges in Boolean Expressions --I don't understand

Jacob Fugal wrote:

> On 5/3/05, Gunnar <gunnar.larsson2@comhem.se> wrote:
>> Hi all
>> I can not make sense of the boolean ranges. The example
>>    (11..20).collect {|i| (i%4==0.. i%3==0)?i:nil} => [nil, 12, nil, nil,
>> nil, 16, 17, 18, nil, 20].
>> 
>> I can figure out all numbers except the '18', which in my opinion should
>> be a 'nil' since i%3==0 is true and would cause the state to change from
>> SET to UNSET. Is the state machine Fig 22.1 correct?
> 
> It appears to me that the second condition in the range UNSETs, but
> inclusively (which makes sense for the semantics of '..'). That's why,
> for example, 12 is printed at all... 12%4==0, so it SETs, retval is
> set to true since it is SET, then 12%3==0 so it UNSETs. But the retval
> is already set, and it returns true, thus printing 12.
> 
> In the same way, when we get to 18, the state machine is already SET
> (since 16). retval is set to true since it is SET, then 18%3==0 so it
> unsets. But just like with 12, retval is already set, so it returns
> true and prints 18.
> 
> For more information see [ruby-talk:91137].
> 
> Jacob Fugal
> 
> [ruby-talk:91137]
> [http://www.ruby-talk.org/cgi-bin/scat.rb/ruby/ruby-talk/91137
OK.
Thank you for answering so very quickly
Gunnar