private void TryParseUnionClause(SparqlQueryParserContext context, GraphPattern p)
{
//Create a new Pattern which will hold the UNION
GraphPattern union = new GraphPattern();
union.IsUnion = true;
//Add the Last Child Pattern of the Parent as that is the start of the UNION
GraphPattern lastchild = p.LastChildPattern();
if (lastchild.IsSimplifiable)
{
union.AddGraphPattern(lastchild.LastChildPattern());
}
else
{
union.AddGraphPattern(lastchild);
}
GraphPattern child = this.TryParseGraphPattern(context, true);
union.AddGraphPattern(child);
//Check for multiple
IToken next = context.Tokens.Peek();
while (next.TokenType == Token.UNION)
{
context.Tokens.Dequeue();
union.AddGraphPattern(this.TryParseGraphPattern(context, true));
next = context.Tokens.Peek();
}
p.AddGraphPattern(union);
}
private void TryParseTriplePatterns(SparqlQueryParserContext context, GraphPattern p)
{
int lasttoken = context.Tokens.LastTokenType;
IToken next = context.Tokens.Dequeue();
//Allowed a Variable/RDF Term/Collection
//OR we might go straight to a OPTIONAL/GRAPH/UNION/FILTER/EXISTS/NOT EXISTS/LET
switch (next.TokenType)
{
case Token.COMMENT:
//Comments are discardable
this.TryParseTriplePatterns(context, p);
break;
case Token.VARIABLE:
//Variable
context.LocalTokens.Push(next);
context.Query.AddVariable(next.Value);
this.TryParsePredicateObjectList(context, p,2);
break;
case Token.URI:
case Token.QNAME:
case Token.LITERAL:
case Token.LONGLITERAL:
case Token.PLAINLITERAL:
//Must then be followed be a non-empty Property List
context.LocalTokens.Push(next);
this.TryParsePredicateObjectList(context, p,2);
break;
case Token.BLANKNODE:
case Token.BLANKNODEWITHID:
//Check list of Blank Node usages
if (context.BlankNodeIDUsages.ContainsKey(next.Value))
{
if (context.BlankNodeIDUsages[next.Value] != context.GraphPatternID)
{
throw ParserHelper.Error("Invalid use of Blank Node Label '" + next.Value + "', this Label has already been used in a different Graph Pattern", next);
}
}
else
{
context.BlankNodeIDUsages.Add(next.Value, context.GraphPatternID);
}
//Must then be followed be a non-empty Property List
context.LocalTokens.Push(next);
this.TryParsePredicateObjectList(context, p, 2);
break;
case Token.LET:
//LET assignment
this.TryParseLetAssignment(context, p);
break;
case Token.BIND:
//BIND assignment
this.TryParseBindAssignment(context, p);
break;
case Token.LEFTSQBRACKET:
//Start of Blank Node Collection
//Create a new Blank Node Token
BlankNodeWithIDToken bnode = new BlankNodeWithIDToken(context.GetNewBlankNodeID(), 0, 0, 0);
//Push twice, once for Subject of Collection
context.LocalTokens.Push(bnode);
next = context.Tokens.Peek();
if (next.TokenType == Token.RIGHTSQBRACKET)
{
//Single anonymous blank node
context.Tokens.Dequeue();
//Parse as Subject of Triples
this.TryParsePredicateObjectList(context, p, 2);
}
else
{
//Parse the Collection
this.TryParsePredicateObjectList(context, p, 2);
//Push again for subject of Triples
context.LocalTokens.Push(bnode);
this.TryParsePredicateObjectList(context, p, 2);
}
break;
case Token.LEFTBRACKET:
//Collection
this.TryParseCollection(context, p, false);
this.TryParsePredicateObjectList(context, p, 2);
break;
case Token.FILTER:
//FILTER Pattern
this.TryParseFilterClause(context, p);
break;
case Token.OPTIONAL:
//OPTIONAL Clause
this.TryParseOptionalClause(context, p);
break;
case Token.EXISTS:
case Token.NOTEXISTS:
case Token.UNSAID:
//EXISTS/NOT EXISTS clause
if (next.TokenType == Token.UNSAID && context.SyntaxMode != SparqlQuerySyntax.Extended) throw new RdfParseException("The UNSAID Keyword is only supported when syntax is set to Extended. It is an alias for NOT EXISTS which can be used when the syntax is set to SPARQL 1.1/Extended");
this.TryParseExistsClause(context, p, (next.TokenType == Token.EXISTS));
break;
case Token.MINUS_P:
//MINUS clause
this.TryParseMinusClause(context, p);
break;
case Token.SERVICE:
//SERVICE clause
this.TryParseServiceClause(context, p);
break;
case Token.SELECT:
//Sub-query
this.TryParseSubquery(context, p);
break;
case Token.GRAPH:
//GRAPH Clause
this.TryParseGraphClause(context, p);
break;
case Token.UNION:
//UNION Clause
this.TryParseUnionClause(context, p);
break;
case Token.LEFTCURLYBRACKET:
//Nested Graph Pattern
p.AddGraphPattern(this.TryParseGraphPattern(context, false));
//Simplify Subqueries
if (p.ChildGraphPatterns.Last().IsSubQuery)
{
GraphPattern temp = p.LastChildPattern();
p.AddTriplePattern(temp.TriplePatterns.First());
}
break;
case Token.DOT:
//Can Discard this if last character was the end of a nested Graph pattern
if (lasttoken == Token.RIGHTCURLYBRACKET || lasttoken == Token.RIGHTBRACKET)
{
//Can Discard this if the next character is not another DOT
next = context.Tokens.Peek();
if (next.TokenType != Token.DOT)
{
if (next.TokenType != Token.RIGHTCURLYBRACKET)
{
this.TryParseTriplePatterns(context, p);
}
else
{
return;
}
}
else
{
throw ParserHelper.Error("A DOT Token cannot follow another DOT Token within a Graph Pattern", next);
}
}
else if (lasttoken == Token.SEMICOLON)
{
//Allow Trailing Semicolon
return;
}
else
{
throw ParserHelper.Error("A DOT Token can only be used to terminate a Triple Pattern or a Nested Graph Pattern", next);
}
break;
default:
throw ParserHelper.Error("Unexpected Token '" + next.GetType().ToString() + "' encountered when the start of a Triple Pattern was expected", next);
}
}
