markus_hanger.rb

#!/usr/bin/ruby

require 'stringio'

class HangMarkus
  attr_reader :solutions
  FILL_IN_CHARACTERS = (32..176).map { |k| k.chr } - [ '_' ]
  def sub_puzzles p
    0 == p.count('_') ?
      p : FILL_IN_CHARACTERS.map { |c| sub_puzzles(p.sub('_', c)) }
  end
  
  def initialize puzzle, expected_output
    @solutions = sub_puzzles(puzzle).flatten.select do |s|
      begin
        $stdout = StringIO.new
        eval(s)
      rescue Exception
      ensure
        $stdout.seek(0)
        matched = ($stdout.read == expected_output)
      end
      matched
    end
    $stdout = STDOUT
  end
end


hanger = HangMarkus.new(<<-END_RUBY, "false\n")
a = 1
b = {nil=>a}
c = b.invert
puts _-_
END_RUBY

hanger.solutions.each_with_index do |solution, i|
  puts "=== Solution #{i} ====="
  puts solution
  puts "\n\n"
end