private IExpression ParseConditionalAlternation()
{
++index; // swallow '('
var expressionOrName = Parse();
if (index == regex.Length || regex[index] != ')')
{
// The Regex constructor should prevent this
throw new InvalidOperationException();
}
++index; // swallow ')'
var item = Parse();
IExpression yes = null;
IExpression no = null;
if (item is IAlternation alternation)
{
if (alternation.Alternatives.Count() > 2)
{
// The Regex constructor should prevent this
throw new InvalidOperationException();
}
yes = alternation.Alternatives.First();
no = alternation.Alternatives.Skip(1).FirstOrDefault();
}
else
{
yes = item;
}
return(ConditionalAlternation.For(expressionOrName, yes, no));
}
/// <summary>
/// Creates an alternation that tries to match the 'yes' option if the expression is matched.
/// </summary>
/// <param name="expression">The expression that must be matched for the 'yes' option to be matched.</param>
/// <param name="yes">The alternative to match if the capture group is matched.</param>
/// <param name="no">The alternative to match if the capture group is not matched.</param>
/// <returns>The alternation.</returns>
public static IConditionalAlternation For(IExpression expression, IExpression yes, IExpression no)
{
if (expression == null)
{
throw new ArgumentNullException(nameof(expression));
}
if (yes == null)
{
throw new ArgumentNullException(nameof(yes));
}
var alternation = new ConditionalAlternation()
{
Expression = expression,
YesOption = yes,
NoOption = no
};
return(alternation);
}
