private IEnumerable <IPgnSymbol> ChildTerminalSymbolsInRange(int start, int length)
{
// Find the first child node that intersects with the given range.
// Can safely call GetChildIndexAfter because of invariant: start < this.Length
int childIndex = GetChildIndexAfter(0 <= start ? start : 0);
int childEndPosition = GetChildStartPosition(childIndex);
while (childIndex < ChildCount && childEndPosition < start + length)
{
int childStartPosition = childEndPosition;
childEndPosition = GetChildStartOrEndPosition(childIndex + 1);
// Skip empty child nodes.
if (childStartPosition < childEndPosition)
{
PgnSyntax childNode = GetChild(childIndex);
if (childNode.IsTerminalSymbol(out IPgnSymbol pgnTerminalSymbol))
{
yield return(pgnTerminalSymbol);
}
else
{
// Translate to relative child position by subtracting childStartPosition.
foreach (var descendant in childNode.ChildTerminalSymbolsInRange(start - childStartPosition, length))
{
yield return(descendant);
}
}
}
childIndex++;
}
}
/// <summary>
/// Initializes as empty.
/// </summary>
public SafeLazyChildSyntaxOrEmpty(PgnSyntax parent, int start)
{
lazyNodeIfNonEmpty = default;
nodeIfEmpty = new PgnEmptySyntax(parent, start);
}
internal PgnEmptySyntax(PgnSyntax parentSyntax, int start)
{
ParentSyntax = parentSyntax;
Start = start;
}