A random generator based on a generalised Backus-Naur Form grammar

Succubus is a generator which takes stochastic paths through a generalised Backus-Naur Form grammar to produce random text. For instance, the following:

grammar = Succubus::Grammar.new do
  add_rule :base, "I have a <colour> <pet>"
  add_rule :colour, "black", "brown", "white"
  add_rule :pet, "cat", "dog", "rabbit"
end
puts grammar.execute :base

...might output I have a black dog. Or I have a brown rabbit. Or any of the other 7 possible combinations of colour and animal.

See the examples/ folder for more sample generators!

Succubus is a RubyGem. That means it's really easy to install. Simply run:

gem install succubus

and you're done.

Succubus is tested against Ruby 1.9.3 and Ruby 2.0 (by Travis - see the little widget up to check we're still passing). I know of no reason it shouldn't work with Ruby 1.8.7 or 1.9.2 - I just haven't got a test environment that works there yet!

Everything you need to make and run your own generators is defined in the Succubus::Grammar class.

To get started:

1. Require in Succubus:

    require 'succubus'
   

2. Create a new instance of Succubus::Grammar, passing it a block:

    require 'succubus'
    grammar = Succubus::Grammar.new do
      # See step 3 for what goes here
    end
   

3. Call add_rule within the block. add_rule takes a symbol which names the rule, followed by one or more strings. When the rule is invoked during grammar execution, exactly one of the strings will be chosen and included in the result text. Text in each string is treated literally, except for instances of <foo>, which instead paste in the result of invoking the rule :foo. Rules can be nested as far as you like!

    require 'succubus'
    grammar = Succubus::Grammar.new do
      add_rule :silly_name, "<title> <adjective><noun>"
      add_rule :title, "Mr.", "Mrs.", "Professor", "Little Miss"
      add_rule :adjective "<smelladj>", "<colour>", "Smarty"
      add_rule :smelladj, "Smelly", "Poopy", "Floral"
      add_rule :colour, "Green", "Purple"
      add_rule :noun, "pants", "brain", "banana", "nose"
    end
   

4. Call execute(<rule>) on your grammar, where <rule> is the symbol naming the top-level rule you want to invoke:

    require 'succubus'
    grammar = Succubus::Grammar.new do
      add_rule :silly_name, "<title> <adjective><noun>"
      add_rule :title, "Mr.", "Mrs.", "Professor", "Little Miss"
      add_rule :adjective, "<smelladj>", "<colour>", "Smarty"
      add_rule :smelladj, "Smelly", "Poopy", "Floral"
      add_rule :colour, "Green", "Purple"
      add_rule :noun, "pants", "brain", "banana", "nose"
    end
    
    puts grammar.execute(:silly_name)
    # Professor Purplepants
   

Oh, why Succubus? Well, Backus-Naur is usually used to describe or verify legal sentences; what you have here is something that uses Backup-Naur to generate sentences. Which is kinda backwards. "Backus", backwards, is "Sukcab"; it's just a short hop from there to Succubus.

I did consider "Bacchus" - a sort of drunken Backus - but the gem name was taken.