@Override
public void meet(Lang node) throws RDFHandlerException {
	Resource currentSubj = subject;
	flushPendingStatement();
	handler.handleStatement(valueFactory.createStatement(subject, RDF.TYPE, SP.LANG));
	predicate = SP.ARG1_PROPERTY;
	node.getArg().visit(this);
	subject = currentSubj;
	predicate = null;
}
 

public Value evaluate(Lang node, BindingSet bindings)
		throws QueryEvaluationException {
	Value argValue = evaluate(node.getArg(), bindings);

	if (argValue instanceof Literal) {
		Literal literal = (Literal) argValue;
		return tripleSource.getValueFactory().createLiteral(literal.getLanguage().orElse(""));
	}

	throw new ValueExprEvaluationException();
}
 

/**
 * Evaluate a {@link Lang} node
 * @param node the node to evaluate
 * @param bindings the set of named value bindings
 * @return a {@link Literal} of the language tag of the {@code Literal} returned by evaluating the argument of the {@code node} or a
 * {code Literal} representing an empty {@code String} if there is no tag
 * @throws ValueExprEvaluationException
 * @throws QueryEvaluationException
 */
private Value evaluate(Lang node, BindingSet bindings) throws ValueExprEvaluationException, QueryEvaluationException {
    Value argValue = evaluate(node.getArg(), bindings);
    if (argValue instanceof Literal) {
        Literal literal = (Literal) argValue;
        Optional<String> langTag = literal.getLanguage();
        if (langTag.isPresent()) {
            return valueFactory.createLiteral(langTag.get());
        }
        return valueFactory.createLiteral("");
    }
    throw new ValueExprEvaluationException();
}
 

/**
 * @inheritDoc
 */
@Override
public void meet(Lang theOp)
        throws Exception
{
    unaryMeet("lang", theOp);
}
 

@Override
public Value evaluate(ValueExpr expr, BindingSet bindings)
		throws QueryEvaluationException {
	if (expr instanceof Var) {
		return evaluate((Var) expr, bindings);
	} else if (expr instanceof ValueConstant) {
		return evaluate((ValueConstant) expr, bindings);
	} else if (expr instanceof BNodeGenerator) {
		return evaluate((BNodeGenerator) expr, bindings);
	} else if (expr instanceof Bound) {
		return evaluate((Bound) expr, bindings);
	} else if (expr instanceof Str) {
		return evaluate((Str) expr, bindings);
	} else if (expr instanceof Label) {
		return evaluate((Label) expr, bindings);
	} else if (expr instanceof Lang) {
		return evaluate((Lang) expr, bindings);
	} else if (expr instanceof LangMatches) {
		return evaluate((LangMatches) expr, bindings);
	} else if (expr instanceof Datatype) {
		return evaluate((Datatype) expr, bindings);
	} else if (expr instanceof Namespace) {
		return evaluate((Namespace) expr, bindings);
	} else if (expr instanceof LocalName) {
		return evaluate((LocalName) expr, bindings);
	} else if (expr instanceof IsResource) {
		return evaluate((IsResource) expr, bindings);
	} else if (expr instanceof IsURI) {
		return evaluate((IsURI) expr, bindings);
	} else if (expr instanceof IsBNode) {
		return evaluate((IsBNode) expr, bindings);
	} else if (expr instanceof IsLiteral) {
		return evaluate((IsLiteral) expr, bindings);
	} else if (expr instanceof IsNumeric) {
		return evaluate((IsNumeric) expr, bindings);
	} else if (expr instanceof IRIFunction) {
		return evaluate((IRIFunction) expr, bindings);
	} else if (expr instanceof Regex) {
		return evaluate((Regex) expr, bindings);
	} else if (expr instanceof Coalesce) {
		return evaluate((Coalesce) expr, bindings);
	} else if (expr instanceof Like) {
		return evaluate((Like) expr, bindings);
	} else if (expr instanceof FunctionCall) {
		return evaluate((FunctionCall) expr, bindings);
	} else if (expr instanceof And) {
		return evaluate((And) expr, bindings);
	} else if (expr instanceof Or) {
		return evaluate((Or) expr, bindings);
	} else if (expr instanceof Not) {
		return evaluate((Not) expr, bindings);
	} else if (expr instanceof SameTerm) {
		return evaluate((SameTerm) expr, bindings);
	} else if (expr instanceof Compare) {
		return evaluate((Compare) expr, bindings);
	} else if (expr instanceof MathExpr) {
		return evaluate((MathExpr) expr, bindings);
	} else if (expr instanceof In) {
		return evaluate((In) expr, bindings);
	} else if (expr instanceof CompareAny) {
		return evaluate((CompareAny) expr, bindings);
	} else if (expr instanceof CompareAll) {
		return evaluate((CompareAll) expr, bindings);
	} else if (expr instanceof Exists) {
		return evaluate((Exists) expr, bindings);
	} else if (expr instanceof If) {
		return evaluate((If) expr, bindings);
	} else if (expr instanceof ListMemberOperator) {
		return evaluate((ListMemberOperator) expr, bindings);
	} else if (expr instanceof ValueExprTripleRef) {
		return evaluate((ValueExprTripleRef) expr, bindings);
	} else if (expr == null) {
		throw new IllegalArgumentException("expr must not be null");
	} else {
		throw new QueryEvaluationException("Unsupported value expr type: " + expr.getClass());
	}
}
 

@Override
public void meet(Lang node) throws X {
	meetUnaryValueOperator(node);
}
 

/**
 * @inheritDoc
 */
@Override
public void meet(Lang theOp) throws Exception {
	unaryMeet("lang", theOp);
}
 

/**
 * @inheritDoc
 */
@Override
public void meet(Lang theOp) throws Exception {
	unaryMeet("lang", theOp);
}
 

public static LangMatches langMatches(String theVar, String theLang) {
	return new LangMatches(new Lang(new Var(theVar)),
			new ValueConstant(SimpleValueFactory.getInstance().createLiteral(theLang)));
}
 

@Override
public Lang visit(ASTLang node, Object data) throws VisitorException {
	ValueExpr arg = (ValueExpr) node.jjtGetChild(0).jjtAccept(this, null);
	return new Lang(arg);
}
 

@Override
public Lang visit(ASTLang node, Object data) throws VisitorException {
	return new Lang((ValueExpr) super.visit(node, data));
}
 

/**
 * Determines which evaluate method to call based on the type of {@link ValueExpr}
 * @param expr the expression to evaluate
 * @param bindings the set of named value bindings the set of named value bindings
 * @return the {@link Value} resulting from the evaluation
 * @throws ValueExprEvaluationException
 * @throws QueryEvaluationException
 */
Value evaluate(ValueExpr expr, BindingSet bindings) throws ValueExprEvaluationException, QueryEvaluationException {
    if (expr instanceof Var) {
        return evaluate((Var) expr, bindings);
    } else if (expr instanceof ValueConstant) {
        return evaluate((ValueConstant) expr, bindings);
    } else if (expr instanceof BNodeGenerator) {
        return evaluate((BNodeGenerator) expr, bindings);
    } else if (expr instanceof Bound) {
        return evaluate((Bound) expr, bindings);
    } else if (expr instanceof Str) {
        return evaluate((Str) expr, bindings);
    } else if (expr instanceof Label) {
        return evaluate((Label) expr, bindings);
    } else if (expr instanceof Lang) {
        return evaluate((Lang) expr, bindings);
    } else if (expr instanceof LangMatches) {
        return evaluate((LangMatches) expr, bindings);
    } else if (expr instanceof Datatype) {
        return evaluate((Datatype) expr, bindings);
    } else if (expr instanceof Namespace) {
        return evaluate((Namespace) expr, bindings);
    } else if (expr instanceof LocalName) {
        return evaluate((LocalName) expr, bindings);
    } else if (expr instanceof IsResource) {
        return evaluate((IsResource) expr, bindings);
    } else if (expr instanceof IsURI) {
        return evaluate((IsURI) expr, bindings);
    } else if (expr instanceof IsBNode) {
        return evaluate((IsBNode) expr, bindings);
    } else if (expr instanceof IsLiteral) {
        return evaluate((IsLiteral) expr, bindings);
    } else if (expr instanceof IsNumeric) {
        return evaluate((IsNumeric) expr, bindings);
    } else if (expr instanceof IRIFunction) {
        return evaluate((IRIFunction) expr, bindings);
    } else if (expr instanceof Regex) {
        return evaluate((Regex) expr, bindings);
    } else if (expr instanceof Coalesce) {
        return evaluate((Coalesce) expr, bindings);
    } else if (expr instanceof Like) {
        return evaluate((Like) expr, bindings);
    } else if (expr instanceof FunctionCall) {
        return evaluate((FunctionCall) expr, bindings);
    } else if (expr instanceof And) {
        return evaluate((And) expr, bindings);
    } else if (expr instanceof Or) {
        return evaluate((Or) expr, bindings);
    } else if (expr instanceof Not) {
        return evaluate((Not) expr, bindings);
    } else if (expr instanceof SameTerm) {
        return evaluate((SameTerm) expr, bindings);
    } else if (expr instanceof Compare) {
        return evaluate((Compare) expr, bindings);
    } else if (expr instanceof MathExpr) {
        return evaluate((MathExpr) expr, bindings);
    } else if (expr instanceof In) {
        return evaluate((In) expr, bindings);
    } else if (expr instanceof CompareAny) {
        return evaluate((CompareAny) expr, bindings);
    } else if (expr instanceof CompareAll) {
        return evaluate((CompareAll) expr, bindings);
    } else if (expr instanceof Exists) {
        return evaluate((Exists) expr, bindings);
    } else if (expr instanceof If) {
        return evaluate((If) expr, bindings);
    } else if (expr instanceof ListMemberOperator) {
        return evaluate((ListMemberOperator) expr, bindings);
    } else if (expr == null) {
        throw new IllegalArgumentException("expr must not be null");
    } else {
        throw new QueryEvaluationException("Unsupported value expr type: " + expr.getClass());
    }
}