Text generator with formal grammar

Grammar definition

First of all you need to define your grammar. Create new Grammar instance and use its methods to add new Rules. Rules are made of Alternatives. Each alternative variant is selected randomly with some given weight. All symbols listed in specific alternative will be printed sequentially.

 var grammar = new Grammar();
 grammar.NewRule("Message",
     new Alternative()
     {
         grammar.NewRule("Greeting",
             new Alternative(new Terminal("Hello"), weight: 1),
             new Alternative(new Terminal("Good morning"), weight: 0.5),
             new Alternative(new Terminal("Good afternoon"), weight: 0.2)
         ),
         new Terminal("! "),
         new NonTerminal("Question"),
         new Terminal("?")
     }
 );
 grammar.NewRule("Question",
    new Alternative(name: "polite question")
    {
         new Terminal("How "),
         grammar.NewRule(
             new Alternative(new Terminal("are you"), weight: 1),
             new Alternative(new Terminal("was your day"), weight: 2),
             new Alternative(new Terminal("do you do"), weight: 0.1)
         ),
    },
    new Alternative(name: "appointment")
    {
         new Terminal("Would you like "),
         grammar.NewRule(
             new Alternative(new Terminal("to go to cinema")),
             new Alternative(new Terminal("to ..."))
         ),
    }
);

Now you can validate and print your grammar like this

grammar.Validate();
Console.WriteLine(grammar.Describe());

<Greeting> ::= "Hello"
             | "Good morning" /*w:0,5*/
             | "Good afternoon" /*w:0,2*/

<Message> ::= <Greeting> "! " <Question> "?"

<Question> ::= "How " <_rule_1> /*n:polite question*/
             | "Would you like " <_rule_2> /*n:appointment*/
[Grammar]
<Greeting> ::= "Hello"
             | "Good morning" /*w:0,5*/
             | "Good afternoon" /*w:0,2*/

<Message> ::= <Greeting> "! " <Question> "?"

<Question> ::= "How " <_rule_1> /*n:polite question*/
             | "Would you like " <_rule_2> /*n:appointment*/

Generation

To generate some text you need to create TextGenerator and pass Grammar instance to it. Then use GenerateWithTree or Generate to create text. Simple message grammar from this example will produce such outputs

var (text, tree) = generator.GenerateWithTree("Message");
Console.WriteLine($"Generated \"{text}\". Production tree\n{tree.Render(grammar: grammar)}\n");

Generated "Good morning! How was your day?". Production tree
<Message>  [alt. 0]
  <Greeting>  [alt. 1]
    "Good morning"
  "! "
  <Question>  [alt. 0]
    "How "
    "was your day"
  "?"

Generated "Hello! Would you like to ...?". Production tree
<Message>  [alt. 0]
  <Greeting>  [alt. 0]
    "Hello"
  "! "
  <Question>  [alt. 1]
    "Would you like "
    "to ..."
  "?"