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The ANTLR 4 grammar compiler.
There is a newer version: 4.13.2
/*
 * [The "BSD license"]
 *  Copyright (c) 2012 Terence Parr
 *  Copyright (c) 2012 Sam Harwell
 *  All rights reserved.
 *
 *  Redistribution and use in source and binary forms, with or without
 *  modification, are permitted provided that the following conditions
 *  are met:
 *
 *  1. Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *  2. Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *  3. The name of the author may not be used to endorse or promote products
 *     derived from this software without specific prior written permission.
 *
 *  THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 *  IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 *  OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 *  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 *  INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 *  NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 *  DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 *  THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 *  (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 *  THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package org.antlr.v4.tool.interp;

import org.antlr.v4.Tool;
import org.antlr.v4.runtime.Parser;
import org.antlr.v4.runtime.ParserRuleContext;
import org.antlr.v4.runtime.TokenStream;
import org.antlr.v4.runtime.atn.ATN;
import org.antlr.v4.runtime.atn.ATNState;
import org.antlr.v4.runtime.atn.DecisionState;
import org.antlr.v4.runtime.atn.ParserATNSimulator;
import org.antlr.v4.runtime.atn.PredictionContextCache;
import org.antlr.v4.runtime.dfa.DFA;
import org.antlr.v4.runtime.misc.NotNull;
import org.antlr.v4.runtime.misc.Nullable;
import org.antlr.v4.tool.Grammar;

public class ParserInterpreter {
	public static class DummyParser extends Parser {
		public final DFA[] decisionToDFA; // not shared for interp
		public final PredictionContextCache sharedContextCache =
			new PredictionContextCache();

		public Grammar g;
		public DummyParser(Grammar g, TokenStream input) {
			super(input);
			this.g = g;
			decisionToDFA = new DFA[100];
		}

		@Override
		public String getGrammarFileName() {
			return null;
		}

		@Override
		public String[] getRuleNames() {
			return g.rules.keySet().toArray(new String[g.rules.size()]);
		}

		@Override
		public String[] getTokenNames() {
			return g.getTokenNames();
		}

		@Override
		public ATN getATN() {
			return null;
		}
		static {
		}
	}

	protected Grammar g;
	public DummyParser parser;
	protected ParserATNSimulator atnSimulator;
	protected TokenStream input;

	public ParserInterpreter(@NotNull Grammar g) {
		this.g = g;
	}

	public ParserInterpreter(@NotNull Grammar g, @NotNull TokenStream input) {
		Tool antlr = new Tool();
		antlr.process(g,false);
		parser = new DummyParser(g, input);
		atnSimulator =
			new ParserATNSimulator(parser, g.atn, parser.decisionToDFA,
										  parser.sharedContextCache);
	}

	public synchronized int predictATN(@NotNull DFA dfa, @NotNull TokenStream input,
									   @Nullable ParserRuleContext outerContext,
									   boolean useContext)
	{
		// sync to ensure this entry doesn't race for dfa access
		return atnSimulator.predictATN(dfa, input, outerContext);
	}

	public int adaptivePredict(@NotNull TokenStream input, int decision,
							   @Nullable ParserRuleContext outerContext)
	{
		return atnSimulator.adaptivePredict(input, decision, outerContext);
	}

	public int matchATN(@NotNull TokenStream input,
						@NotNull ATNState startState)
	{
		if (startState.getNumberOfTransitions() == 1) {
			return 1;
		}
		else if (startState instanceof DecisionState) {
			return atnSimulator.adaptivePredict(input, ((DecisionState)startState).decision, null);
		}
		else if (startState.getNumberOfTransitions() > 0) {
			return 1;
		}
		else {
			return -1;
		}
	}

	public ParserATNSimulator getATNSimulator() {
		return atnSimulator;
	}

}