/// <summary> /// Folds a character terminal node. /// </summary> /// <param name="characterTerminal"></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>?VisitCharacterTerminal(CharacterTerminal characterTerminal, TArgument argument) => characterTerminal;
/// <inheritdoc />
protected override GrammarNode <Char>?VisitAlternation(Alternation <Char> alternation, OptimizeArgs argument)
{
var nodes = alternation.GrammarNodes.Select(node => this.Visit(node, argument))
.Where(node => node is not null)
.ToList();
var matchedCharTerminals = new HashSet <Char>();
var matchedStringTerminals = new HashSet <String>();
var matchedCharRanges = new HashSet <Range <Char> >();
var matchedUnicodeCategories = new HashSet <UnicodeCategory>();
var matchedNodes = new HashSet <GrammarNode <Char> >(GrammarTreeStructuralComparer.Instance);
for (var nodeIdx = 0; nodeIdx < nodes.Count; nodeIdx++)
{
loopStart:
GrammarNode <Char> currentNode = nodes[nodeIdx] !;
if (matchedNodes.Contains(currentNode))
{
nodes.RemoveAt(nodeIdx);
goto loopStart;
}
switch (currentNode.Kind)
{
case GrammarNodeKind.CharacterStringTerminal:
{
var strTerminal = (StringTerminal)currentNode;
if (matchedStringTerminals.Contains(strTerminal.Value))
{
nodes.RemoveAt(nodeIdx);
goto loopStart;
}
matchedStringTerminals.Add(strTerminal.Value);
break;
}
case GrammarNodeKind.CharacterTerminal:
{
var ch = ((CharacterTerminal)currentNode).Value;
if (isCharMatched(ch))
{
nodes.RemoveAt(nodeIdx);
goto loopStart;
}
matchedCharTerminals.Add(ch);
break;
}
case GrammarNodeKind.CharacterRange:
{
var characterRange = (CharacterRange)currentNode;
var newStart = characterRange.Range.Start;
while (isCharMatched(newStart) &&
newStart <= characterRange.Range.End)
{
newStart++;
}
var newEnd = characterRange.Range.End;
while (isCharMatched(newEnd) &&
newEnd >= newStart)
{
newEnd--;
}
// The new start will be greater than the new end if all characters in the
// range are already being matched.
if (newStart > newEnd)
{
nodes.RemoveAt(nodeIdx);
goto loopStart;
}
else if (newStart == newEnd)
{
nodes[nodeIdx] = new CharacterTerminal(newStart);
goto loopStart;
}
else if (characterRange.Range.Start != newStart || characterRange.Range.End != newEnd)
{
nodes[nodeIdx] =
currentNode =
characterRange = new CharacterRange(newStart, newEnd);
}
break;
}
}
matchedNodes.Add(currentNode);
}
if (nodes.Count == 0)
{
return(null);
}
else if (nodes.Count == 1)
{
return(nodes[0]);
}
else if (nodes.SequenceEqual(alternation.GrammarNodes))
{
return(alternation);
}
else
{
return(new Alternation <Char>(nodes !));
}
Boolean isCharMatched(Char ch) =>
matchedCharTerminals !.Contains(ch) ||
matchedCharRanges !.Any(range => CharUtils.IsInRange(range.Start, ch, range.End)) ||
matchedUnicodeCategories !.Contains(Char.GetUnicodeCategory(ch));
}
protected override String?VisitCharacterTerminal(CharacterTerminal characterTerminal, Unit argument) => Char.ToString(characterTerminal.Value);
/// <summary> /// Visits a character terminal. /// </summary> /// <param name="characterTerminal"></param> /// <param name="argument">The argument data passed by the caller.</param> /// <returns>The result of visiting this node.</returns> protected abstract TReturn VisitCharacterTerminal(CharacterTerminal characterTerminal, TArgument argument);