Pastable version of Combinatorial explosion with continuations

<pre class='prettyprint' language='ruby'>$c = []
def fork_reality(*l)
  callcc {|c| $c &lt;&lt; c }
  $c.pop if l.size &lt;= 1
  l.shift
end

def collect_realities
  $c.last.call until $c.empty?
end

def contract_sentence(arr, index = 0, res = [])
  return res.compact.join(' ') if index == arr.size 
  skip = 1
  x = arr[index]
  nxt = arr[index+1]
  nxt2 = arr[index+2]
  r = case
  when x == 'a' &amp;&amp; (nxt =~ /^[aeiuo]/ || nxt =~ /^hono/ || nxt =~ /^honest/ || nxt =~ /^hour/)
    'an'
  when x == 'I' &amp;&amp; nxt == 'am'
    skip = 2
    fork_reality(&quot;I'm&quot;, &quot;I am&quot;)
  when %w(you we they).include?(x) &amp;&amp; %w(are have).include?(nxt) &amp;&amp; nxt2 == 'not'
    skip = 3
    fork_reality(&quot;#{x}'#{nxt[-2,2]} not&quot;, &quot;#{x} #{nxt}n't&quot;, &quot;#{x} #{nxt} not&quot;)
  when %w(you we they).include?(x) &amp;&amp; %w(are have).include?(nxt)
    skip = 3
    fork_reality(&quot;#{x}'re&quot;, &quot;#{x} #{nxt}&quot;)
  when %w(he she it).include?(x) &amp;&amp; %w(is has).include?(nxt) &amp;&amp; nxt2 == 'not'
    skip = 3
    fork_reality(&quot;#{x} #{nxt}n't&quot;, &quot;#{x} #{nxt} not&quot;)
  when %w(he she it).include?(x) &amp;&amp; %w(is has).include?(nxt)
    skip = 2
    fork_reality(&quot;#{x}'s&quot;, &quot;#{x} #{nxt}&quot;)
  when %w(is are).include?(x) &amp;&amp; nxt == 'not'
    skip = 2
    fork_reality(&quot;#{x}n't&quot;, &quot;#{x} #{nxt}&quot;)
  else
    x
  end
  contract_sentence(arr, index + skip, res + [r])
end

r = []

r &lt;&lt; contract_sentence(%w(I am green but you are not white and Bob is not a honest man while Alice and Ina are not purple))

collect_realities

raise unless r.include? &quot;I'm green but you aren't white and Bob isn't an honest man while Alice and Ina aren't purple&quot;
raise unless r.include? &quot;I'm green but you are not white and Bob is not an honest man while Alice and Ina are not purple&quot;
raise unless r.include? &quot;I am green but you are not white and Bob is not an honest man while Alice and Ina aren't purple&quot;

p r</pre>
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Pastable version of Combinatorial explosion with continuations