From: ptkwt@... (Phil Tomson)
Date: 2004-01-31T16:54:55+09:00
Subject: flip flop operator and assignment

I'm working on the pattern matching section for 
http://pleac.sourceforge.net/pleac_ruby/t1.html  (an attempt to duplicate 
the Perl Cookbook for several languages including Ruby).

The Perl code that needs to be duplicated in Ruby is:
while (<>) {
    $in_header =   1  .. /^$/;
    $in_body   = /^$/ .. eof();
}


In Ruby first I tried:

File.open("filename"){|f|
  f.each_line {|l|
    in_header = $.==1 .. l=~/^$/
    in_body   = l=~/^$/ .. f.eof
    puts "in_header: #{l}" if in_header
    puts "in_body: #{l}" if in_body
  }
}

But that give the following error:
ArgumentError: bad value for range

However, when I changed it to use the ternary operator, like so:

  File.open("filename"){|f|
    f.each_line {|l|
      in_header = $.==1 .. l=~/^$/ ? true : false
      in_body   = l=~/^$/ .. f.eof ? true : false
      puts "in_header: #{l}" if in_header
      puts "in_body: #{l}" if in_body
    }
  }

It then works.

What gives?  It seems that the flip/flop operator is evaluating to true or 
false, why can't I just assign that value to in_header or in_body?

Phil