/// <summary>
/// Genereates warnings for useless variables.
/// </summary>
/// <param name="g">the grammar</param>
/// <returns></returns>
public static List <string> getGrammarWarnings(ContextFreeGrammar g)
{
List <string> res = new List <string>();
HashSet <string> variables = new HashSet <string>();
foreach (var n in g.Variables)
{
variables.Add(n.ToString());
}
var productiv = g.GetUsefulNonterminals(true);
var unproductiv = variables.Except(productiv);
if (unproductiv.Count() > 0)
{
res.Add(string.Format("Warning: There are unproductive variables! ({0})", string.Join(", ", unproductiv)));
}
var reachable = new HashSet <string>();
//Lemma 4.2, p. 89, Hopcroft-Ullman
Stack <Nonterminal> stack = new Stack <Nonterminal>();
stack.Push(g.StartSymbol);
reachable.Add(g.StartSymbol.ToString());
while (stack.Count > 0)
{
Nonterminal v = stack.Pop();
foreach (Production p in g.GetProductions(v))
{
foreach (Nonterminal u in p.GetVariables())
{
if (!reachable.Contains(u.ToString()))
{
reachable.Add(u.ToString());
stack.Push(u);
}
}
}
}
var unreachable = variables.Except(reachable);
if (unproductiv.Count() > 0)
{
res.Add(string.Format("Warning: There are unreachable variables! ({0})", string.Join(", ", unreachable)));
}
return(res);
}