From: james.d.masters@...
Date: 2007-04-16T06:40:07+09:00
Subject: Re: Ruby Truth Table Generator

On Apr 15, 9:21 am, "Stephen Duncan" <stephen.dun...@gmail.com> wrote:
> I'd like to say I just whipped this up, but I'm still a Ruby-newbie,
> so this took me a few days.  I'd love to get some feedback on the
> code...

After looking at the code, it looks like the @string instance variable
and the methods generate_values and get_next are used only once and
are used for building a string representation of the truth table.  I'd
recommend doing away with these and do the calculation in to_s (this
could open the possibility of changing the formula after object
creation if you wanted to enhance this class to allow dynamic
formulas).  In any case, I would recommend counting through
possibilities and using a bitwise mask to figure out the permutations
instead of using the generate_values method:

class TruthTable
  def initialize(formula, &expression)
    @formula = formula
    @expression = expression
    @variables = @formula.gsub(/[^[:alpha:]\s]/, " ").split.uniq
    @expression ||= eval("Proc.new {|#{@variables.join(',')}|
#{formula} }")
  end

  def to_s
    # create a mask for each of the variables
    var_masks = (0..@variables.length-1).to_a.reverse.map {|i| 2**i}

    # create header
    str = @variables.join("\t") + "\t#{@formula}\n"

    # Go through all permutations of variables
    0.upto(2**@variables.length-1) do |cnt_mask|
      # compare the count mask versus each variable mask - map as
values
      values = var_masks.map {|var_mask| (var_mask & cnt_mask) ==
var_mask}
      str += values.join("\t") + "\t#{@expression.call(*values)}" +
"\n"
    end

    str
  end
end

As for the overall concept of this class, I did something similar a
while back and used the same technique that you did - accept a string
to allow a visual representation and then eval the formula within a
Proc.new.