/// <summary>
/// Generates a CNF for a given grammar or returns null if the Grammar doesn't produce any words.
/// </summary>
/// <param name="g">the original grammar</param>
/// <returns>the CNF or null</returns>
public static ContextFreeGrammar getEquivalentCNF(ContextFreeGrammar g)
{
if (g == null)
{
return(null);
}
if (g.IsInCNF())
{
return(g);
}
try
{
ContextFreeGrammar res = ContextFreeGrammar.MkCNF(g);
//handle empty string
res.setAcceptanceForEmptyString(g.acceptsEmptyString());
return(res);
}
catch (AutomataException e)
{
if (g.acceptsEmptyString())
{
var res = new ContextFreeGrammar(new Nonterminal("S"), new Production[] { new Production(new Nonterminal("S"), new GrammarSymbol[] { new Nonterminal("S"), new Nonterminal("S") }) });
res.setAcceptanceForEmptyString(true);
return(res);
}
return(null);
}
}