public Rule(IEnumerable <Chain> chains, NonTerminalSymbol target)
{
if (chains == null)
{
throw new ArgumentNullException(nameof(chains));
}
if (target == null)
{
throw new ArgumentNullException(nameof(target));
}
Chains = chains.ToSortedSet().AsReadOnly();
if (!Chains.Any())
{
throw new ArgumentException("Rule must contain at least one chain.");
}
if (Chains.AnyNull())
{
throw new ArgumentException("At least one null chain was found.");
}
Alphabet = Chains.SelectMany(chain => chain.Alphabet).ToSortedSet().AsReadOnly();
Target = target;
ISet <NonTerminalSymbol> nonTerminals = Chains.SelectMany(chain => chain.NonTerminals).ToSortedSet();
nonTerminals.Add(Target);
NonTerminals = nonTerminals.AsReadOnly();
}