truth.rb

truth.rb

#!/usr/bin/env ruby

class Object
  def > other  # implication operator: false > true == true
    if self == true or self == false
      !self or other
    else
      super
    end
  end
end

class FalseClass ; def to_01 ; "0" ; end ; end
class TrueClass ;  def to_01 ; "1" ; end ; end

class TruthTable
  attr_reader :map, :results

  def initialize &block
    raise ArgumentError, "block expected", caller unless block
    raise ArgumentError, "block should not take arguments" if block.arity > 0

    @counter = 0
    @map = []
    @results = []

    until @counter == 2 ** @map.size
      @results << instance_eval(&block)
      @counter += 1
    end
  end

  def method_missing name
    index = @map.index name
    if index
      mask = 2 ** index
      @counter & mask != 0
    else
      @map << name
      false
    end
  end
end

def truth_table &block
  truth_table = TruthTable.new &block
  map = truth_table.map
  results = truth_table.results
  n = map.size
  puts map.join " "
  f = "%0#{n}b"
  lines = []
  for i in 0...2**n
    a_s = (f % i).reverse
    a_a = a_s.split("").map{|c| c != "0"}
    inputs = map.map(&:size).each_with_index.map{|s,i| "%-#{s}s" % a_a[i].to_01}.join " "
    output = results[i].to_01
    lines << "#{inputs} => #{output}"
  end
  puts lines.sort
end

alias tt truth_table

Example usage: ruby -r ./truth.rb -e 'tt { a and not b }'

Implication: ruby -r ./truth.rb -e 'tt { this > that }'

Creating a “truth table” is not hard, you can use an useful tool (CKod, at http://ckod.sourceforge.net/_/) to make a “truth table”.

1. CKod homepage: http://ckod.sourceforge.net/
2. CKod online: http://ckod.sourceforge.net/_/
3. CKod forum: http://ckod.sourceforge.net/~/

Good luck to you!