private void AddRule(Variable variable, params Symbol[] symbols)
{
if (!_rules.ContainsKey(variable))
_rules.Add(variable, new List<IEnumerable<Symbol>>());
if (!_rules[variable].Any(r => r.IsEquivalentTo(symbols)))
_rules[variable].Add(symbols);
}
private ChomskyNormalFormTransformer(Variable startVariable, IDictionary<Variable, ICollection<IEnumerable<Symbol>>> rules)
{
_rules = new Dictionary<Variable, ICollection<IEnumerable<Symbol>>>();
rules.ForEach(p =>
{
_rules.Add(p.Key, new List<IEnumerable<Symbol>>());
p.Value.ForEach(r => _rules[p.Key].Add(r));
});
_startVariable = GetNewVariableBasedOn(startVariable);
AddRule(_startVariable, startVariable);
}
private IEnumerable<Terminal> GetTerminalsProducedByVariable(Variable variable)
{
return _terminalsProducedByVariables[variable];
}
public ContextFreeGrammar Produce(Variable variable, params Symbol[] symbols)
{
AddRule(variable, symbols);
return this;
}
public IEnumerable<IEnumerable<Symbol>> GetRules(Variable variable)
{
return _rules.ContainsKey(variable) ? _rules[variable] : Enumerable.Empty<IEnumerable<Symbol>>();
}
public ContextFreeGrammar(Variable startVariable, IDictionary<Variable, ICollection<IEnumerable<Symbol>>> rules)
{
_startVariable = startVariable;
_rules = rules;
}
private void AddRule(Variable variable, params Symbol[] symbols)
{
if (symbols.Count() == 1 && variable.Equals(symbols.Single()))
throw new ArgumentException("Recursive unit rules cannot be created.");
if (!_rules.ContainsKey(variable))
{
_rules.Add(variable, new List<IEnumerable<Symbol>>());
}
_rules[variable].Add(symbols);
}
public static ContextFreeGrammar Transform(Variable startVariable, IDictionary<Variable, ICollection<IEnumerable<Symbol>>> rules)
{
var transformer = new ChomskyNormalFormTransformer(startVariable, rules);
return transformer.Transform();
}
private void ReplaceVariable(Variable variable, params Symbol[] replacement)
{
var variableContainingRuleCollections = _rules.Values.Where(r => r.Any(x => x.Contains(variable))).ToArray();
foreach (var collection in variableContainingRuleCollections)
{
collection.ToArray().ForEach(i => collection.AddRange(i.ReplacePermutations(variable, replacement)));
}
}
private void RemoveRule(Variable variable, params Symbol[] symbols)
{
if (!_rules.ContainsKey(variable)) return;
_rules[variable].Where(r => r.IsEquivalentTo(symbols)).ToArray()
.ForEach(r => _rules[variable].Remove(r));
}
private Variable GetNewVariableBasedOn(Variable original)
{
if (!Variables.Contains(original)) return original;
for (var i = 0; ; i++)
{
Variable variable = String.Format("{0}_{1}", original, i);
if (!Variables.Contains(variable)) return variable;
}
}
