From: Brian Candler <b.candler@...>
Date: 2008-12-01T23:46:11+09:00
Subject: Re: Control Structures

Like many languages, there are lots of ways to do things. Using a block 
with Array.new lets you initialise an Array with n elements in one go, 
where the block is invoked n times to create each element.

I think that comparing monkey == monkey.sort is the easiest way to check 
for values in sequence, but a more esoteric way is using 
Enumerable#each_cons to check each pair in turn.

So this gives the following solution:

require 'enumerator'
puts "How many elements?"
a = Integer(gets)

loop do
  monkey = Array.new(a) { rand(a) }
  out_of_order = false
  monkey.each_cons(2) { |x,y|
    if x > y
      out_of_order = true
      break
    end
  }
  puts "#{monkey.inspect}, out_of_order=#{out_of_order}"
end

Now, you can squeeze this a bit more, because each_cons normally returns 
nil, but break can pass a different return value. This gives:

loop do
  monkey = Array.new(a) { rand(a) }
  out_of_order = monkey.each_cons(2) { |x,y|
    break true if x > y
  }
  puts "#{monkey.inspect}, out_of_order=#{out_of_order ? "yes" : "no"}"
end

Now, to get really funky. The Enumerable module has a bunch of methods 
for operating on sequences of objects which are yielded by the 'each' 
method. Using to_enum you can insert a proxy object which maps the call 
to #each to a call to another method - such as #each_cons. So then you 
get:

loop do
  monkey = Array.new(a) { rand(a) }
  out_of_order = monkey.to_enum(:each_cons,2).find { |x,y| x > y }
  puts "#{monkey.inspect} #{out_of_order && "bad monkey!"}"
end

I certainly wouldn't have written that as a newcomer to Ruby :-) But 
it's nice to know that, when you have mastered the basics, there's lots 
more to chew on.

Regards,

Brian.

P.S. Try all this stuff in irb. For example, to try out each_cons:

irb(main):001:0> require 'enumerator'
=> true
irb(main):002:0> [1,2,3,4,5].each_cons(2) { |x| p x }
[1, 2]
[2, 3]
[3, 4]
[4, 5]
=> nil
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