A closure containing a pure function

closure_containing_pure_function.rb

=begin
  Functions containing no free/unbound variables are called pure functions.
  Functions containing one or more free variables are called closures.
 
  Adapted from the quick exercise in https://leanpub.com/javascript-allonge/read#closures
  In turn, this is adapted from https://gist.github.com/zealoushacker/8091614
 
  If pure functions can contain closures, can a closure contain a pure function? 
  Attempt to compose a closure that contains a pure function.
  
  Many thanks to @raganwald!
=end
 
lambda do |x| 
  lambda do |y| 
    lambda { |n| n }
    return x
  end
end["foo"]["bar"]