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/*
* Copyright (c) 2012-2017 The ANTLR Project. All rights reserved.
* Use of this file is governed by the BSD 3-clause license that
* can be found in the LICENSE.txt file in the project root.
*/
package org.antlr.v4.runtime.tree;
import org.antlr.v4.runtime.ParserRuleContext;
import org.antlr.v4.runtime.RuleContext;
public class ParseTreeWalker {
public static final ParseTreeWalker DEFAULT = new ParseTreeWalker();
public void walk(ParseTreeListener listener, ParseTree t) {
if ( t instanceof ErrorNode) {
listener.visitErrorNode((ErrorNode)t);
return;
}
else if ( t instanceof TerminalNode) {
listener.visitTerminal((TerminalNode)t);
return;
}
RuleNode r = (RuleNode)t;
enterRule(listener, r);
int n = r.getChildCount();
for (int i = 0; i<n; i++) {
walk(listener, r.getChild(i));
}
exitRule(listener, r);
}
/**
* The discovery of a rule node, involves sending two events: the generic
* {@link ParseTreeListener#enterEveryRule} and a
* {@link RuleContext}-specific event. First we trigger the generic and then
* the rule specific. We to them in reverse order upon finishing the node.
*/
protected void enterRule(ParseTreeListener listener, RuleNode r) {
ParserRuleContext ctx = (ParserRuleContext)r.getRuleContext();
listener.enterEveryRule(ctx);
ctx.enterRule(listener);
}
protected void exitRule(ParseTreeListener listener, RuleNode r) {
ParserRuleContext ctx = (ParserRuleContext)r.getRuleContext();
ctx.exitRule(listener);
listener.exitEveryRule(ctx);
}
}
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