Ruby.

gistfile1.rb

class Foo
  def some_method
    puts "In some_method"
    def some_other_method
      puts "In some other method"
      "Foo"
    end
    "Bar"
  end
end

foo = Foo.new
foo.some_method

# In some_method
# => "Bar"

foo.some_other_method

#In some other method
#=> "Foo"

class Bar
  def some_method
    def some_other_method
      "OK"
    end
  end
end

Bar.new.some_other_method
# NoMethodError: undefined method `some_other_method' for #<Bar:0x000001009bf680>
       
Bar.new.some_method
# => nil 

Bar.new.some_other_method
# => OK

class Baz
  def some_method
    some_var = "x"
    def some_other_method
      some_other_var = "y"
      "#{some_var}, #{some_other_var}"
    end
  end
end

baz = Baz.new
baz.some_method
baz.some_other_method

# NameError: undefined local variable or method `some_var' for #<Baz:0x000001010ae2c0>