/// <summary>
/// Folds a positive lookahead node.
/// </summary>
/// <param name="lookahead"></param>
/// <param name="argument">The argument to be passed to the visitor method.</param>
/// <returns>
/// <list type="number">
/// <item>The original node if it's to be kept</item>
/// <item>A different node to replace the original node with</item>
/// <item>Null if the node is to be removed</item>
/// </list>
/// </returns>
protected override GrammarNode <Char>?VisitPositiveLookahead(PositiveLookahead lookahead, TArgument argument)
{
if (lookahead is null)
{
throw new ArgumentNullException(nameof(lookahead));
}
GrammarNode <Char>?innerNode = this.Visit(lookahead.InnerNode, argument);
if (innerNode is null)
{
return(null);
}
else if (innerNode == lookahead.InnerNode)
{
return(lookahead);
}
else
{
return(new PositiveLookahead(innerNode));
}
}
protected override String?VisitPositiveLookahead(PositiveLookahead positiveLookahead, Unit argument) => this.Visit(positiveLookahead.InnerNode, default);
/// <summary> /// Visits a lookahead. /// </summary> /// <param name="positiveLookahead"></param> /// <param name="argument">The argument data passed by the caller.</param> /// <returns>The result of visiting this node.</returns> protected abstract TReturn VisitPositiveLookahead(PositiveLookahead positiveLookahead, TArgument argument);
