```ruby
require 'spec_helper'

describe 'memoized rules' do
  specify 'memoized symbol prefix' do
    direction = Calyx::Grammar.new(123) do
      rule :start, "Enter {character}. Exit {character}."
      rule :character, :@name
      rule :name, "Vladimir", "Estragon"
    end

    10.times do
      expect(direction.generate).to eq("Enter Vladimir. Exit Vladimir.")
    end
  end
end
```

Add additional tests of memoized symbols in template strings
user
```ruby
require 'spec_helper'

describe 'memoized rules' do
  specify 'memoized symbol prefix' do
    grammar = Calyx::Grammar.new do
      rule :start, "Enter {character}. Exit {character}."
      rule :character, :@name
      rule :name, "Vladimir", "Estragon"
    end

    expect(grammar.generate).to eq(grammar.generate)
  end

  specify 'memoized template expression' do
    grammar = Calyx::Grammar.new do
      rule :burger, "Monolith {@extras}"
      rule :burger_combo, "Jumbo Monolith {@extras}"
      rule :extras, "w/ extra grease", "w/ polycheese"
    end

    expect(grammar.generate(:burger_combo)).to include(grammar.generate(:burger))
  end
end
```
assistant