public static Match <Lexem> NextOrThrow(IMatchIterator <Lexem> iterator)
{
if (!iterator.TryMatchNext(out var match))
{
throw CreateException("unrecognized character", iterator.Position);
}
return(match);
}
public static Node MatchSequence(IMatchIterator <Lexem> iterator, Match <Lexem> match, bool atTopLevel)
{
var nodes = new List <Node>();
while (true)
{
// Match literal character or character class
Node node;
switch (match.Value.Type)
{
case LexemType.ClassBegin:
node = MatchClass(iterator, NextOrThrow(iterator));
break;
case LexemType.End:
if (atTopLevel)
{
return(Node.CreateSequence(nodes));
}
throw CreateException("unfinished sequence", iterator.Position);
case LexemType.Escape:
node = Node.CreateCharacter(match.Value.Replacement);
break;
case LexemType.Wildcard:
node = Wildcard;
break;
case LexemType.ZeroOrMore:
node = Node.CreateRepeat(Wildcard, 0, -1);
break;
default:
node = Node.CreateCharacter(match.Capture[0]);
break;
}
match = NextOrThrow(iterator);
nodes.Add(node);
}
}
private static (int min, int max) MatchRepeat(IMatchIterator <Lexem> iterator, Match <Lexem> match)
{
var buffer = new StringBuilder();
while (match.Value.Type == LexemType.Digit)
{
buffer.Append(match.Capture[0]);
match = NextOrThrow(iterator);
}
int max;
var min = buffer.Length > 0 ? int.Parse(buffer.ToString()) : 0;
if (match.Value.Type == LexemType.Comma)
{
buffer.Clear();
match = NextOrThrow(iterator);
while (match.Value.Type == LexemType.Digit)
{
buffer.Append(match.Capture[0]);
match = NextOrThrow(iterator);
}
max = buffer.Length > 0 ? int.Parse(buffer.ToString()) : -1;
if (max >= 0 && max < min)
{
throw CreateException("invalid repeat sequence", iterator.Position);
}
}
else
{
max = min;
}
if (match.Value.Type != LexemType.RepeatEnd)
{
throw CreateException("expected end of repeat specifier", iterator.Position);
}
return(min, max);
}
public static (Node, Match <Lexem>) MatchAlternative(IMatchIterator <Lexem> iterator, Match <Lexem> match, bool atTopLevel)
{
var alternativeNodes = new List <Node>();
while (true)
{
var(sequenceNodes, nextMatch) = MatchSequence(iterator, match, atTopLevel);
alternativeNodes.Add(sequenceNodes);
if (nextMatch.Value.Type != LexemType.Alternative)
{
return(Node.CreateAlternative(alternativeNodes), nextMatch);
}
match = NextOrThrow(iterator);
}
}
public static (Node, Match <Lexem>) MatchSequence(IMatchIterator <Lexem> iterator, Match <Lexem> match, bool atTopLevel)
{
var sequenceNodes = new List <Node>();
while (true)
{
// Match literal character or character class
Match <Lexem> nextMatch;
Node node;
switch (match.Value.Type)
{
case LexemType.Alternative:
return(Node.CreateSequence(sequenceNodes), match);
case LexemType.End:
if (!atTopLevel)
{
throw CreateException("unfinished parenthesis", iterator.Position);
}
return(Node.CreateSequence(sequenceNodes), match);
case LexemType.ClassBegin:
node = MatchClass(iterator, NextOrThrow(iterator));
nextMatch = NextOrThrow(iterator);
break;
case LexemType.Escape:
node = Node.CreateCharacter(match.Value.Replacement);
nextMatch = NextOrThrow(iterator);
break;
case LexemType.SequenceBegin:
var(alternativeNode, alternativeNextMatch) = MatchAlternative(iterator, NextOrThrow(iterator), false);
node = alternativeNode;
nextMatch = alternativeNextMatch;
break;
case LexemType.SequenceEnd:
if (!atTopLevel)
{
return(Node.CreateSequence(sequenceNodes), NextOrThrow(iterator));
}
node = Node.CreateCharacter(match.Capture[0]);
nextMatch = NextOrThrow(iterator);
break;
case LexemType.Wildcard:
node = Node.CreateCharacter(new[] { new NodeRange(char.MinValue, char.MaxValue) });
nextMatch = NextOrThrow(iterator);
break;
default:
node = Node.CreateCharacter(match.Capture[0]);
nextMatch = NextOrThrow(iterator);
break;
}
// Match repeat specifier if any
int max;
int min;
switch (nextMatch.Value.Type)
{
case LexemType.OneOrMore:
(min, max) = (1, -1);
match = NextOrThrow(iterator);
break;
case LexemType.RepeatBegin:
(min, max) = MatchRepeat(iterator, NextOrThrow(iterator));
match = NextOrThrow(iterator);
break;
case LexemType.ZeroOrMore:
(min, max) = (0, -1);
match = NextOrThrow(iterator);
break;
case LexemType.ZeroOrOne:
(min, max) = (0, 1);
match = NextOrThrow(iterator);
break;
default:
(min, max) = (1, 1);
match = nextMatch;
break;
}
sequenceNodes.Add(Node.CreateRepeat(node, min, max));
}
}
private static Node MatchClass(IMatchIterator <Lexem> iterator, Match <Lexem> match)
{
var ranges = new List <NodeRange>();
// Allow first character of a class to be special "negate class" character
if (match.Value.Type == LexemType.Negate)
{
throw new NotImplementedException("negated character classes are not supported yet");
}
// Allow first (or post-negate) character of a class to be literal "end of class" character
if (match.Value.Type == LexemType.ClassEnd)
{
ranges.Add(new NodeRange(match.Capture[0], match.Capture[0]));
match = NextOrThrow(iterator);
}
while (true)
{
// Match next character, which may later be considered as the
// beginning character of range
char begin;
char end;
switch (match.Value.Type)
{
case LexemType.End:
throw CreateException("unfinished characters class", iterator.Position);
case LexemType.ClassEnd:
return(Node.CreateCharacter(ranges));
case LexemType.Escape:
begin = match.Value.Replacement;
break;
default:
begin = match.Capture[0];
break;
}
match = NextOrThrow(iterator);
// If next lexem defines a range (e.g. "a-z"), read next one to
// get end character for this range before registering it
if (match.Value.Type == LexemType.Range)
{
match = NextOrThrow(iterator);
switch (match.Value.Type)
{
case LexemType.End:
throw CreateException("unfinished characters class", iterator.Position);
case LexemType.Escape:
end = match.Value.Replacement;
break;
default:
end = match.Capture[0];
break;
}
match = NextOrThrow(iterator);
}
// Otherwise register transition from a single character
else
{
end = begin;
}
ranges.Add(new NodeRange(begin, end));
}
}
/// <Summary> /// Compile regular pattern into graph of non-deterministic states leading to given value. /// </Summary> protected abstract Node CreateGraph(IMatchIterator <Lexem> iterator);
