# coding: utf-8

i = 0
increment_function = lambda do
  puts "Incrementing from #{i} to #{i+1}"
  i += 1
end
decrement_function = lambda do
  i -= 1
  puts "Decrementing from #{i+1} to #{i}"
end
increment_function.call
decrement_function.call
increment_function.call
increment_function.call
decrement_function.call

=begin 
From the book, Ch.8 page 217 (p. 240 of the PDF): 

Each block you pass to the lambdas accesses the same variable in the
parent scope. Ruby achieves this by checking whether the EP already
points to the heap. If so, as with the second call to lambda in
Listing 8-15, Ruby won’t create a second copy; it will simply reuse
the same rb_env_t structure in the second rb_proc_t
structure. Ultimately, both lambdas use the same heap copy of the
stack.

Suggestion: find the code responsible for this logic in the actual 
Ruby source!
=end