closures.rb

# easy example
def multiplier n
  lambda { |m| n*m }
end

# advanced examples
class Proc
  def * other
    lambda { |*args| self.call(*other.call(*args)) } # other is variable form enclosing scope
  end
  
  def ** n
    lambda { |*args| (n.times.map { self }.inject(:*)).call(*args) } # n is variable form enclosing scope
  end
end

require "test/unit"

class TestLambdas < Test::Unit::TestCase
  def test_multiplier
    times_5 = multiplier(5)
    assert_equal times_5.call(3), 5 * 3
  end
  
  def test_composition
    f = lambda { |x| x**2 }
    assert_equal (f*f)[3], 3**4
  end
  
  def test_exp
    f = lambda { |x| x**2 }
    assert_equal (f**3)[3], (f*f*f)[3]
  end
  
end