/*
* $Id$
*
* Copyright (C) 2003-2015 JNode.org
*
* This library is free software; you can redistribute it and/or modify it
* under the terms of the GNU Lesser General Public License as published
* by the Free Software Foundation; either version 2.1 of the License, or
* (at your option) any later version.
*
* This library is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
* License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this library; If not, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
package org.jnode.shell.syntax;
/**
* A MuBackReference is a placeholder for another MuSyntax node. Its intended use is for
* representing cycles in a syntax graph; e.g. in " <a-seq> ::= 'a' | 'a' <a-seq> ",
* the <a-seq> on the RHS would initially be represented by a MuBackReference.
* <p>
* Back references must be resolved by calling resolveBackReferences() on the syntax tree root
* before the parse(...) method is called.
*
* @author crawley@jnode.org
*/
public class MuBackReference extends MuSyntax {
public MuBackReference(String label) {
super(label);
if (label.length() == 0) {
throw new IllegalArgumentException("empty label");
}
}
@Override
String format(FormatState state) {
return "<" + label + ">";
}
@Override
public MuSyntaxKind getKind() {
return MuSyntaxKind.BACK_REFERENCE;
}
@Override
MuSyntax resolveBackReferences(ResolveState state) throws SyntaxFailureException {
MuSyntax target = state.refMap.get(label);
if (target == null) {
throw new SyntaxFailureException("Cannot resolve '" + label + "'");
}
return target;
}
}