test_tco.rb

require 'minitest/autorun'

###
# Test to demonstrate TCO in Ruby.  Tested in 1.9.2+
class TestTCO < MiniTest::Unit::TestCase
  code = <<-eocode
    class Facts
      def fact_helper(n, res)
        if n == 1
          res
        else
          fact_helper(n - 1, n * res)
        end
      end
      def fact(n)
        fact_helper(n, 1)
      end
    end
  eocode

  eval code
  RubyVM::InstructionSequence.compile_option = {
    :tailcall_optimization => true,
    :trace_instruction     => false
  }

  # Any code you want with TCO should happen after you've tweaked compile_option
  eval code.sub(/Facts/, 'TCOFacts')

  FACTSIZE = 30_000

  def test_exception
    assert_raises(SystemStackError) do
      Facts.new.fact(FACTSIZE)
    end
  end

  def test_tco
    assert TCOFacts.new.fact(FACTSIZE)
  end
end