From: "David A. Black" <dblack@...>
Date: 2004-10-30T06:13:39+09:00
Subject: Re: Another scrach on head

Hi --

On Sat, 30 Oct 2004, Mohammad Khan wrote:

> On Fri, 2004-10-29 at 14:38, Jamis Buck wrote:
> 
> > No, I mispoke for the sake of simplification. nil and false _evaluate to 
> > false_ in a boolean context, and everything else evaluates to _true_ in 
> > a boolean context.
> > 
> > Thus
> > 
> >    puts "here" if false
> >    puts "there" if nil
> > 
> > would print nothing, whereas
> > 
> >    puts "here" if true
> >    puts "there" if 5
> >    puts "everywhere" if 1 && Object.new && :foobar
> > 
> > would print
> > 
> >    here
> >    there
> >    everywhere
> > 
> > Hope that is clearer.
> > 
> > - Jamis
> 
> In other words
> 
> a = Whatever.new
> 
> puts "a is nil"                    if a.nil?
> puts "a is neither nil, nor false" if a
> puts "a is true"                   if a == true
> puts "a is false"                  if a == false
> puts "a is nil again!"             if a == nil

You could also say

  puts "a is true"                   if a
  puts "a is false"                  if a.nil?

in the Boolean sense of true/false.  Ruby provides the constants TRUE
and FALSE, for the respective objects; this might be a good way to
write your example (and my additions):

puts "a is nil"                    if a.nil?
puts "a is neither nil, 
     nor false, nor FALSE"         if a
puts "a is TRUE"                   if a == TRUE
puts "a is true"                   if a
puts "a is FALSE"                  if a == FALSE
puts "a is false"                  if not a
puts "a is nil again!"             if a == nil
puts "a is false"                  if a.nil?

Here, I'm using 'true/false' to mean Boolean true/false, and
TRUE/FALSE to mean the objects.  


David

-- 
David A. Black
dblack@wobblini.net