private IExpression Parse()
{
var alternatives = new List <IExpression>();
var expression = new CompoundExpression();
while (index != regex.Length)
{
if (regex[index] == '|')
{
++index;
alternatives.Add(expression.Normalize());
expression = new CompoundExpression();
}
else
{
var item = ParseInternal();
if (item == null)
{
break;
}
expression.Add(item);
}
}
if (alternatives.Count == 0)
{
return(expression.Normalize());
}
else
{
alternatives.Add(expression.Normalize());
return(Alternation.From(alternatives));
}
}
/// <summary>
/// Creates an alternation consisting of the given alternatives.
/// </summary>
/// <param name="alternatives">The alternatives comprising the alternation.</param>
/// <returns>The alternation.</returns>
public static IAlternation From(IEnumerable <IExpression> alternatives)
{
if (alternatives == null)
{
throw new ArgumentNullException(nameof(alternatives));
}
var alternation = new Alternation();
foreach (var alternative in alternatives)
{
alternation.Add(alternative);
}
return(alternation);
}