public ContextFreeGrammar(string[] nonterminals, string[] terminals,
ProductionInfo[] rules, string starting)
{
if (HasDuplicates(nonterminals))
throw new ArgumentException("Nonterminal symbols cannot contain duplicates.");
if (HasDuplicates(terminals))
throw new ArgumentException("Terminal symbols cannot contain duplicates.");
if (HasDuplicates(rules))
throw new ArgumentException("Rules cannot contain duplicates.");
bool overlap = terminals.Intersect(nonterminals).Any();
if (overlap)
throw new ArgumentException("Terminal symbols and nonterminal symbols are not disjoint.");
var symbolByString = new Dictionary<string, GrammarSymbol>(nonterminals.Length + terminals.Length);
this.nonterminals = new GrammarSymbol[nonterminals.Length];
for (int i = 0; i < nonterminals.Length; i++)
{
this.nonterminals[i] = new GrammarSymbol(nonterminals[i], false);
symbolByString.Add(nonterminals[i], this.nonterminals[i]);
}
this.terminals = new GrammarSymbol[terminals.Length];
for (int i = 0; i < terminals.Length; i++)
{
this.terminals[i] = new GrammarSymbol(terminals[i], true);
symbolByString.Add(terminals[i], this.terminals[i]);
}
this.alphabet = (this.nonterminals).Concat(this.terminals).ToArray();
int startingIndex = Array.IndexOf(nonterminals, starting);
if (startingIndex < 0)
throw new ArgumentException("Start symbol must be a nonterminal symbol.");
this.starting = this.nonterminals[startingIndex];
var ruleList = new List<Production>(rules.Length);
foreach (var rule in rules)
{
if (!IsValid(rule))
throw new ArgumentException("Production rule is invalid.");
GrammarSymbol original = symbolByString[rule.Original];
var sentenceSymbols = new List<GrammarSymbol>();
foreach (string s in rule.DirectDerivative)
sentenceSymbols.Add(symbolByString[s]);
Sentence sentence = new Sentence(sentenceSymbols.ToArray());
ruleList.Add(new Production(original, sentence));
}
this.rules = ruleList.ToArray();
}
private bool IsValid(ProductionInfo production)
{
Debug.Assert(nonterminals != null);
Debug.Assert(terminals != null);
Debug.Assert(alphabet != null);
if (!AlphabetContains(nonterminals, production.Original))
{
return(false);
}
foreach (var symbol in production.DirectDerivative)
{
if (!AlphabetContains(alphabet, symbol))
{
return(false);
}
}
return(true);
}
private static void EnterRules()
{
if (nonterminals == null || terminals == null)
{
Console.WriteLine("Please enter nonterminal and terminal symbols first.");
return;
}
if (alphabet == null)
{
alphabet = nonterminals.Concat(terminals).ToArray();
}
string message = "Enter number of production rules: ";
int rulesCount = AskForNumberInput(message, 1);
rules = new ProductionInfo[rulesCount];
for (int i = 0; i < rulesCount; i++)
{
message = string.Format("Enter original symbol of production rule number {0}: ", i + 1);
string original = AskForSymbolInput(message, nonterminals);
message = "Enter number of symbol in the sentence: ";
int symbolsCount = AskForNumberInput(message, 0);
string[] sentence = new string[symbolsCount];
for (int j = 0; j < symbolsCount; j++)
{
message = string.Format("Enter the symbol number {0}: ", j + 1);
sentence[j] = AskForSymbolInput(message, alphabet);
}
rules[i] = new ProductionInfo(original, sentence);
}
grammar = new ContextFreeGrammar(nonterminals, terminals, rules, starting);
normalForm = grammar.GetChomskyNormalForm();
}
private bool IsValid(ProductionInfo production)
{
Debug.Assert(nonterminals != null);
Debug.Assert(terminals != null);
Debug.Assert(alphabet != null);
if (!AlphabetContains(nonterminals, production.Original))
return false;
foreach (var symbol in production.DirectDerivative)
if (!AlphabetContains(alphabet, symbol))
return false;
return true;
}
private bool HasDuplicates(ProductionInfo[] rules)
{
int n = rules.Length;
for (int i = 0; i < n - 1; i++)
for (int j = i + 1; j < n; j++)
if (rules[i] == rules[j])
return true;
return false;
}
private static void EnterRules()
{
if (nonterminals == null || terminals == null)
{
Console.WriteLine("Please enter nonterminal and terminal symbols first.");
return;
}
if (alphabet == null)
alphabet = nonterminals.Concat(terminals).ToArray();
string message = "Enter number of production rules: ";
int rulesCount = AskForNumberInput(message, 1);
rules = new ProductionInfo[rulesCount];
for (int i = 0; i < rulesCount; i++)
{
message = string.Format("Enter original symbol of production rule number {0}: ", i + 1);
string original = AskForSymbolInput(message, nonterminals);
message = "Enter number of symbol in the sentence: ";
int symbolsCount = AskForNumberInput(message, 0);
string[] sentence = new string[symbolsCount];
for (int j = 0; j < symbolsCount; j++)
{
message = string.Format("Enter the symbol number {0}: ", j + 1);
sentence[j] = AskForSymbolInput(message, alphabet);
}
rules[i] = new ProductionInfo(original, sentence);
}
grammar = new ContextFreeGrammar(nonterminals, terminals, rules, starting);
normalForm = grammar.GetChomskyNormalForm();
}
