chain.rb

class Array
  def chain m
    r = shift
    each{|n| r = r.send(m, n)}
    r
  end
end

class Range
  def chain m
    to_a.chain m
  end
end

practice_factorial.rb

#= Practice::factorial
# 1 *2 *3 *.. *n

require "chain"

module Practice

  def factorial1 n
    n == 1 ? 1 : n * factorial1(n - 1)
  end

  def factorial2 n
    (1..n).chain :*
  end
end