private ContextFreeGrammar(GrammarSymbol[] nonterminals, GrammarSymbol[] terminals,
Production[] rules, GrammarSymbol starting)
{
// doesnt check for exception, careful
this.nonterminals = nonterminals;
this.terminals = terminals;
this.alphabet = nonterminals.Concat(terminals).ToArray();
this.rules = rules;
this.starting = starting;
}
public ContextFreeGrammar GetChomskyNormalForm()
{
var newNonterminals = new List<GrammarSymbol>(nonterminals);
var newRules = new List<Production>(rules);
var toBeAddedRules = new List<Production>();
var newStarting = new GrammarSymbol("S0", false);
newNonterminals.Add(newStarting);
newRules.Add(new Production(newStarting, new Sentence(new[] { starting })));
for (int i = 0; i < newRules.Count; i++)
{
var rule = newRules[i];
var sentence = rule.DirectDerivative.ToArray();
if (rule.DirectDerivative.HasNonsolitaryTerminal)
{
var encountered = new List<GrammarSymbol>();
for (int j = 0; j < sentence.Length; j++)
{
var symbol = sentence[j];
if (symbol.IsTerminal)
{
string label = "N" + symbol.ToString();
GrammarSymbol newSymbol = encountered.FirstOrDefault((s) => s.Matches(label));
if (newSymbol == null)
{
newSymbol = new GrammarSymbol(label, false);
encountered.Add(newSymbol);
newNonterminals.Add(newSymbol);
toBeAddedRules.Add(new Production(newSymbol, new Sentence(new[] { symbol })));
}
sentence[j] = newSymbol;
}
}
}
newRules[i] = new Production(rule.Original, new Sentence(sentence));
}
newRules.AddRange(toBeAddedRules);
toBeAddedRules = new List<Production>();
for (int i = 0; i < newRules.Count; i++)
{
var rule = newRules[i];
var sentence = rule.DirectDerivative;
var newSentence = sentence.ToArray();
if (sentence.HasMoreThanTwoNonterminals)
{
GrammarSymbol nextSymbol = rule.Original;
int n = newSentence.Length;
for (int j = 0; j < n - 2; j++)
{
var currentSymbol = nextSymbol;
nextSymbol = new GrammarSymbol(rule.Original.ToString() + (i + 1).ToString(), false);
newNonterminals.Add(nextSymbol);
toBeAddedRules.Add(new Production(currentSymbol, new Sentence(new[] { newSentence[j], nextSymbol })));
}
newRules[i] = new Production(nextSymbol, new Sentence(new[] { newSentence[n - 2], newSentence[n - 1] }));
// order is somewhat scrambled
}
}
newRules.AddRange(toBeAddedRules);
toBeAddedRules = new List<Production>();
bool noEpsilonLeft = false;
while (!noEpsilonLeft)
{
noEpsilonLeft = true;
foreach (var rule in newRules)
if (rule.DirectDerivative.IsEmpty && rule.Original != newStarting)
{
GrammarSymbol nullable = rule.Original;
bool isLastRule = newRules.Count((r) => r.Original == nullable) == 0;
if (!isLastRule)
for (int i = 0; i < newRules.Count(); i++)
{
var oldSymbol = newRules[i].Original;
var sentence = newRules[i].DirectDerivative.ToArray();
int n = sentence.Length;
Debug.Assert(n < 3);
if (n == 1 && sentence[0] == nullable)
AddIfNotExist(ref newRules, new Production(oldSymbol, Sentence.Empty));
else if (n == 2)
{
if (sentence[0] == sentence[1] && sentence[0] == nullable)
{
AddIfNotExist(ref newRules, new Production(oldSymbol, Sentence.Empty));
AddIfNotExist(ref newRules, new Production(oldSymbol, new Sentence(new[] { sentence[0] })));
}
else if (sentence[0] == nullable)
AddIfNotExist(ref newRules, new Production(oldSymbol, new Sentence(new[] { sentence[1] })));
else if (sentence[1] == nullable)
AddIfNotExist(ref newRules, new Production(oldSymbol, new Sentence(new[] { sentence[0] })));
}
}
else
{
for (int i = 0; i < newRules.Count(); i++)
{
var oldSymbol = newRules[i].Original;
var sentence = newRules[i].DirectDerivative.ToArray();
int n = sentence.Length;
Debug.Assert(n < 3);
if (n == 1 && sentence[0] == nullable)
AddIfNotExist(ref newRules, new Production(oldSymbol, Sentence.Empty));
else if (n == 2)
{
if (sentence[0] == sentence[1] && sentence[0] == nullable)
AddIfNotExist(ref newRules, new Production(oldSymbol, Sentence.Empty));
else if (sentence[0] == nullable)
AddIfNotExist(ref newRules, new Production(oldSymbol, new Sentence(new[] { sentence[1] })));
else
AddIfNotExist(ref newRules, new Production(oldSymbol, new Sentence(new[] { sentence[0] })));
}
}
newNonterminals.Remove(nullable);
}
newRules.Remove(rule);
toBeAddedRules = new List<Production>();
noEpsilonLeft = false;
break;
}
}
bool noUnitRuleLeft = false;
while (!noUnitRuleLeft)
{
noUnitRuleLeft = true;
foreach (var rule in newRules)
{
bool isUnitRule = rule.DirectDerivative.Length == 1 && !rule.DirectDerivative.First().IsTerminal;
if (isUnitRule)
{
newRules.Remove(rule);
var toBeReplaced = rule.DirectDerivative.First();
var replacement = rule.Original;
for (int i = 0; i < newRules.Count(); i++)
{
var oldSymbol = newRules[i].Original;
var sentence = newRules[i].DirectDerivative.ToArray();
if (oldSymbol == toBeReplaced)
toBeAddedRules.Add(new Production(replacement, new Sentence(sentence)));
}
newNonterminals.Remove(toBeReplaced);
newRules.AddRange(toBeAddedRules);
toBeAddedRules = new List<Production>();
noUnitRuleLeft = false;
break;
}
}
}
return new ContextFreeGrammar(newNonterminals.ToArray(), this.terminals, newRules.ToArray(), newStarting);
}
private void AddIfNotExist(ref List<Production> newRules, Production toBeAdded)
{
foreach (Production rule in newRules)
if (rule.Original == toBeAdded.Original
&& rule.DirectDerivative.SequenceEqual(toBeAdded.DirectDerivative))
return;
newRules.Add(toBeAdded);
}
public ContextFreeGrammar GetChomskyNormalForm()
{
var newNonterminals = new List <GrammarSymbol>(nonterminals);
var newRules = new List <Production>(rules);
var toBeAddedRules = new List <Production>();
var newStarting = new GrammarSymbol("S0", false);
newNonterminals.Add(newStarting);
newRules.Add(new Production(newStarting, new Sentence(new[] { starting })));
for (int i = 0; i < newRules.Count; i++)
{
var rule = newRules[i];
var sentence = rule.DirectDerivative.ToArray();
if (rule.DirectDerivative.HasNonsolitaryTerminal)
{
var encountered = new List <GrammarSymbol>();
for (int j = 0; j < sentence.Length; j++)
{
var symbol = sentence[j];
if (symbol.IsTerminal)
{
string label = "N" + symbol.ToString();
GrammarSymbol newSymbol = encountered.FirstOrDefault((s) => s.Matches(label));
if (newSymbol == null)
{
newSymbol = new GrammarSymbol(label, false);
encountered.Add(newSymbol);
newNonterminals.Add(newSymbol);
toBeAddedRules.Add(new Production(newSymbol, new Sentence(new[] { symbol })));
}
sentence[j] = newSymbol;
}
}
}
newRules[i] = new Production(rule.Original, new Sentence(sentence));
}
newRules.AddRange(toBeAddedRules);
toBeAddedRules = new List <Production>();
for (int i = 0; i < newRules.Count; i++)
{
var rule = newRules[i];
var sentence = rule.DirectDerivative;
var newSentence = sentence.ToArray();
if (sentence.HasMoreThanTwoNonterminals)
{
GrammarSymbol nextSymbol = rule.Original;
int n = newSentence.Length;
for (int j = 0; j < n - 2; j++)
{
var currentSymbol = nextSymbol;
nextSymbol = new GrammarSymbol(rule.Original.ToString() + (i + 1).ToString(), false);
newNonterminals.Add(nextSymbol);
toBeAddedRules.Add(new Production(currentSymbol, new Sentence(new[] { newSentence[j], nextSymbol })));
}
newRules[i] = new Production(nextSymbol, new Sentence(new[] { newSentence[n - 2], newSentence[n - 1] }));
// order is somewhat scrambled
}
}
newRules.AddRange(toBeAddedRules);
toBeAddedRules = new List <Production>();
bool noEpsilonLeft = false;
while (!noEpsilonLeft)
{
noEpsilonLeft = true;
foreach (var rule in newRules)
{
if (rule.DirectDerivative.IsEmpty && rule.Original != newStarting)
{
GrammarSymbol nullable = rule.Original;
bool isLastRule = newRules.Count((r) => r.Original == nullable) == 0;
if (!isLastRule)
{
for (int i = 0; i < newRules.Count(); i++)
{
var oldSymbol = newRules[i].Original;
var sentence = newRules[i].DirectDerivative.ToArray();
int n = sentence.Length;
Debug.Assert(n < 3);
if (n == 1 && sentence[0] == nullable)
{
AddIfNotExist(ref newRules, new Production(oldSymbol, Sentence.Empty));
}
else if (n == 2)
{
if (sentence[0] == sentence[1] && sentence[0] == nullable)
{
AddIfNotExist(ref newRules, new Production(oldSymbol, Sentence.Empty));
AddIfNotExist(ref newRules, new Production(oldSymbol, new Sentence(new[] { sentence[0] })));
}
else if (sentence[0] == nullable)
{
AddIfNotExist(ref newRules, new Production(oldSymbol, new Sentence(new[] { sentence[1] })));
}
else if (sentence[1] == nullable)
{
AddIfNotExist(ref newRules, new Production(oldSymbol, new Sentence(new[] { sentence[0] })));
}
}
}
}
else
{
for (int i = 0; i < newRules.Count(); i++)
{
var oldSymbol = newRules[i].Original;
var sentence = newRules[i].DirectDerivative.ToArray();
int n = sentence.Length;
Debug.Assert(n < 3);
if (n == 1 && sentence[0] == nullable)
{
AddIfNotExist(ref newRules, new Production(oldSymbol, Sentence.Empty));
}
else if (n == 2)
{
if (sentence[0] == sentence[1] && sentence[0] == nullable)
{
AddIfNotExist(ref newRules, new Production(oldSymbol, Sentence.Empty));
}
else if (sentence[0] == nullable)
{
AddIfNotExist(ref newRules, new Production(oldSymbol, new Sentence(new[] { sentence[1] })));
}
else
{
AddIfNotExist(ref newRules, new Production(oldSymbol, new Sentence(new[] { sentence[0] })));
}
}
}
newNonterminals.Remove(nullable);
}
newRules.Remove(rule);
toBeAddedRules = new List <Production>();
noEpsilonLeft = false;
break;
}
}
}
bool noUnitRuleLeft = false;
while (!noUnitRuleLeft)
{
noUnitRuleLeft = true;
foreach (var rule in newRules)
{
bool isUnitRule = rule.DirectDerivative.Length == 1 && !rule.DirectDerivative.First().IsTerminal;
if (isUnitRule)
{
newRules.Remove(rule);
var toBeReplaced = rule.DirectDerivative.First();
var replacement = rule.Original;
for (int i = 0; i < newRules.Count(); i++)
{
var oldSymbol = newRules[i].Original;
var sentence = newRules[i].DirectDerivative.ToArray();
if (oldSymbol == toBeReplaced)
{
toBeAddedRules.Add(new Production(replacement, new Sentence(sentence)));
}
}
newNonterminals.Remove(toBeReplaced);
newRules.AddRange(toBeAddedRules);
toBeAddedRules = new List <Production>();
noUnitRuleLeft = false;
break;
}
}
}
return(new ContextFreeGrammar(newNonterminals.ToArray(), this.terminals, newRules.ToArray(), newStarting));
}