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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
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 *  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.
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 *  INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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package org.antlr.v4.codegen.model;

import org.antlr.v4.codegen.OutputModelFactory;
import org.antlr.v4.runtime.atn.DecisionState;
import org.antlr.v4.runtime.misc.IntervalSet;
import org.antlr.v4.tool.ast.GrammarAST;

import java.util.List;

/** (A B C)? */
public class LL1OptionalBlockSingleAlt extends LL1Choice {
	@ModelElement public SrcOp expr;
	@ModelElement public List followExpr; // might not work in template if size>1

	public LL1OptionalBlockSingleAlt(OutputModelFactory factory,
									 GrammarAST blkAST,
									 List alts)
	{
		super(factory, blkAST, alts);
		this.decision = ((DecisionState)blkAST.atnState).decision;

		/** Lookahead for each alt 1..n */
//		IntervalSet[] altLookSets = LinearApproximator.getLL1LookaheadSets(dfa);
		IntervalSet[] altLookSets = factory.getGrammar().decisionLOOK.get(decision);
		altLook = getAltLookaheadAsStringLists(altLookSets);
		IntervalSet look = altLookSets[0];
		IntervalSet followLook = altLookSets[1];

		IntervalSet expecting = look.or(followLook);
		this.error = getThrowNoViableAlt(factory, blkAST, expecting);

		expr = addCodeForLookaheadTempVar(look);
		followExpr = factory.getLL1Test(followLook, blkAST);
	}
}