http://www.antlr.org/antlr4-runtime: The ANTLR 4 Runtime (ANTLR) 
/*
 * 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;

import org.antlr.v4.runtime.atn.ATNConfigSet;
import org.antlr.v4.runtime.atn.DecisionInfo;
import org.antlr.v4.runtime.atn.ParserATNSimulator;
import org.antlr.v4.runtime.atn.PredictionMode;
import org.antlr.v4.runtime.dfa.DFA;

import java.util.BitSet;


How to emit recognition errors. 
/** How to emit recognition errors. */
public interface ANTLRErrorListener {
	
Upon syntax error, notify any interested parties. This is not how to recover from errors or compute error messages. ANTLRErrorStrategy specifies how to recover from syntax errors and how to compute error messages. This listener's job is simply to emit a computed message, though it has enough information to create its own message in many cases. 
The RecognitionException is non-null for all syntax errors except when we discover mismatched token errors that we can recover from in-line, without returning from the surrounding rule (via the single token insertion and deletion mechanism).


Params:
  • recognizer – 
       What parser got the error. From this
		  object, you can access the context as well
		  as the input stream.
  • offendingSymbol –  The offending token in the input token stream, unless recognizer is a lexer (then it's null). If no viable alternative error, e has token at which we started production for the decision.
  • line – 
		  The line number in the input where the error occurred.
  • charPositionInLine – 
		  The character position within that line where the error occurred.
  • msg – 
		  The message to emit.
  • e – 
       The exception generated by the parser that led to
       the reporting of an error. It is null in the case where
       the parser was able to recover in line without exiting the
       surrounding rule.
/**
	 * Upon syntax error, notify any interested parties. This is not how to
	 * recover from errors or compute error messages. {@link ANTLRErrorStrategy}
	 * specifies how to recover from syntax errors and how to compute error
	 * messages. This listener's job is simply to emit a computed message,
	 * though it has enough information to create its own message in many cases.
	 *
	 * <p>The {@link RecognitionException} is non-null for all syntax errors except
	 * when we discover mismatched token errors that we can recover from
	 * in-line, without returning from the surrounding rule (via the single
	 * token insertion and deletion mechanism).</p>
	 *
	 * @param recognizer
     *        What parser got the error. From this
	 * 		  object, you can access the context as well
	 * 		  as the input stream.
	 * @param offendingSymbol
	 *        The offending token in the input token
	 * 		  stream, unless recognizer is a lexer (then it's null). If
	 * 		  no viable alternative error, {@code e} has token at which we
	 * 		  started production for the decision.
	 * @param line
	 * 		  The line number in the input where the error occurred.
	 * @param charPositionInLine
	 * 		  The character position within that line where the error occurred.
	 * @param msg
	 * 		  The message to emit.
	 * @param e
	 *        The exception generated by the parser that led to
	 *        the reporting of an error. It is null in the case where
	 *        the parser was able to recover in line without exiting the
	 *        surrounding rule.
	 */
	public void syntaxError(Recognizer<?, ?> recognizer,
							Object offendingSymbol,
							int line,
							int charPositionInLine,
							String msg,
							RecognitionException e);

	
This method is called by the parser when a full-context prediction
results in an ambiguity.

Each full-context prediction which does not result in a syntax error will call either reportContextSensitivity or reportAmbiguity.


When ambigAlts is not null, it contains the set of potentially viable alternatives identified by the prediction algorithm. When ambigAlts is null, use ATNConfigSet.getAlts to obtain the represented alternatives from the configs argument.


When exact is true, all of the potentially viable alternatives are truly viable, i.e. this is reporting an exact ambiguity. When exact is false, at least two of
the potentially viable alternatives are viable for the current input, but
the prediction algorithm terminated as soon as it determined that at
least the minimum potentially viable alternative is truly
viable.


When the PredictionMode.LL_EXACT_AMBIG_DETECTION prediction mode is used, the parser is required to identify exact ambiguities so exact will always be true.


This method is not used by lexers.


Params:
  • recognizer – the parser instance
  • dfa – the DFA for the current decision
  • startIndex – the input index where the decision started
  • stopIndex – the input input where the ambiguity was identified
  • exact – true if the ambiguity is exactly known, otherwise false. This is always true when PredictionMode.LL_EXACT_AMBIG_DETECTION is used.
  • ambigAlts – the potentially ambiguous alternatives, or null to indicate that the potentially ambiguous alternatives are the complete set of represented alternatives in configs
  • configs – the ATN configuration set where the ambiguity was
identified
/**
	 * This method is called by the parser when a full-context prediction
	 * results in an ambiguity.
	 *
	 * <p>Each full-context prediction which does not result in a syntax error
	 * will call either {@link #reportContextSensitivity} or
	 * {@link #reportAmbiguity}.</p>
	 *
	 * <p>When {@code ambigAlts} is not null, it contains the set of potentially
	 * viable alternatives identified by the prediction algorithm. When
	 * {@code ambigAlts} is null, use {@link ATNConfigSet#getAlts} to obtain the
	 * represented alternatives from the {@code configs} argument.</p>
	 *
	 * <p>When {@code exact} is {@code true}, <em>all</em> of the potentially
	 * viable alternatives are truly viable, i.e. this is reporting an exact
	 * ambiguity. When {@code exact} is {@code false}, <em>at least two</em> of
	 * the potentially viable alternatives are viable for the current input, but
	 * the prediction algorithm terminated as soon as it determined that at
	 * least the <em>minimum</em> potentially viable alternative is truly
	 * viable.</p>
	 *
	 * <p>When the {@link PredictionMode#LL_EXACT_AMBIG_DETECTION} prediction
	 * mode is used, the parser is required to identify exact ambiguities so
	 * {@code exact} will always be {@code true}.</p>
	 *
	 * <p>This method is not used by lexers.</p>
	 *
	 * @param recognizer the parser instance
	 * @param dfa the DFA for the current decision
	 * @param startIndex the input index where the decision started
	 * @param stopIndex the input input where the ambiguity was identified
	 * @param exact {@code true} if the ambiguity is exactly known, otherwise
	 * {@code false}. This is always {@code true} when
	 * {@link PredictionMode#LL_EXACT_AMBIG_DETECTION} is used.
	 * @param ambigAlts the potentially ambiguous alternatives, or {@code null}
	 * to indicate that the potentially ambiguous alternatives are the complete
	 * set of represented alternatives in {@code configs}
	 * @param configs the ATN configuration set where the ambiguity was
	 * identified
	 */
	void reportAmbiguity(Parser recognizer,
						 DFA dfa,
						 int startIndex,
						 int stopIndex,
						 boolean exact,
						 BitSet ambigAlts,
						 ATNConfigSet configs);

	
This method is called when an SLL conflict occurs and the parser is about
to use the full context information to make an LL decision.

If one or more configurations in configs contains a semantic predicate, the predicates are evaluated before this method is called. The subset of alternatives which are still viable after predicates are evaluated is reported in conflictingAlts.


This method is not used by lexers.


Params:
  • recognizer – the parser instance
  • dfa – the DFA for the current decision
  • startIndex – the input index where the decision started
  • stopIndex – the input index where the SLL conflict occurred
  • conflictingAlts – The specific conflicting alternatives. If this is null, the conflicting alternatives are all alternatives represented in configs. At the moment, conflictingAlts is non-null (for the reference implementation, but Sam's optimized version can see this as null).
  • configs – the ATN configuration set where the SLL conflict was
detected
/**
	 * This method is called when an SLL conflict occurs and the parser is about
	 * to use the full context information to make an LL decision.
	 *
	 * <p>If one or more configurations in {@code configs} contains a semantic
	 * predicate, the predicates are evaluated before this method is called. The
	 * subset of alternatives which are still viable after predicates are
	 * evaluated is reported in {@code conflictingAlts}.</p>
	 *
	 * <p>This method is not used by lexers.</p>
	 *
	 * @param recognizer the parser instance
	 * @param dfa the DFA for the current decision
	 * @param startIndex the input index where the decision started
	 * @param stopIndex the input index where the SLL conflict occurred
	 * @param conflictingAlts The specific conflicting alternatives. If this is
	 * {@code null}, the conflicting alternatives are all alternatives
	 * represented in {@code configs}. At the moment, conflictingAlts is non-null
	 * (for the reference implementation, but Sam's optimized version can see this
	 * as null).
	 * @param configs the ATN configuration set where the SLL conflict was
	 * detected
	 */
	void reportAttemptingFullContext(Parser recognizer,
									 DFA dfa,
									 int startIndex,
									 int stopIndex,
									 BitSet conflictingAlts,
									 ATNConfigSet configs);

	
This method is called by the parser when a full-context prediction has a
unique result.

Each full-context prediction which does not result in a syntax error will call either reportContextSensitivity or reportAmbiguity.


For prediction implementations that only evaluate full-context predictions when an SLL conflict is found (including the default ParserATNSimulator implementation), this method reports cases where SLL conflicts were resolved to unique full-context predictions, i.e. the decision was context-sensitive. This report does not necessarily indicate a problem, and it may appear even in completely unambiguous grammars.


configs may have more than one represented alternative if the full-context prediction algorithm does not evaluate predicates before beginning the full-context prediction. In all cases, the final prediction is passed as the prediction argument.


Note that the definition of "context sensitivity" in this method differs from the concept in DecisionInfo.contextSensitivities. This method reports all instances where an SLL conflict occurred but LL parsing produced a unique result, whether or not that unique result matches the minimum alternative in the SLL conflicting set.


This method is not used by lexers.


Params:
  • recognizer – the parser instance
  • dfa – the DFA for the current decision
  • startIndex – the input index where the decision started
  • stopIndex – the input index where the context sensitivity was
finally determined
  • prediction – the unambiguous result of the full-context prediction
  • configs – the ATN configuration set where the unambiguous prediction
was determined
/**
	 * This method is called by the parser when a full-context prediction has a
	 * unique result.
	 *
	 * <p>Each full-context prediction which does not result in a syntax error
	 * will call either {@link #reportContextSensitivity} or
	 * {@link #reportAmbiguity}.</p>
	 *
	 * <p>For prediction implementations that only evaluate full-context
	 * predictions when an SLL conflict is found (including the default
	 * {@link ParserATNSimulator} implementation), this method reports cases
	 * where SLL conflicts were resolved to unique full-context predictions,
	 * i.e. the decision was context-sensitive. This report does not necessarily
	 * indicate a problem, and it may appear even in completely unambiguous
	 * grammars.</p>
	 *
	 * <p>{@code configs} may have more than one represented alternative if the
	 * full-context prediction algorithm does not evaluate predicates before
	 * beginning the full-context prediction. In all cases, the final prediction
	 * is passed as the {@code prediction} argument.</p>
	 *
	 * <p>Note that the definition of "context sensitivity" in this method
	 * differs from the concept in {@link DecisionInfo#contextSensitivities}.
	 * This method reports all instances where an SLL conflict occurred but LL
	 * parsing produced a unique result, whether or not that unique result
	 * matches the minimum alternative in the SLL conflicting set.</p>
	 *
	 * <p>This method is not used by lexers.</p>
	 *
	 * @param recognizer the parser instance
	 * @param dfa the DFA for the current decision
	 * @param startIndex the input index where the decision started
	 * @param stopIndex the input index where the context sensitivity was
	 * finally determined
	 * @param prediction the unambiguous result of the full-context prediction
	 * @param configs the ATN configuration set where the unambiguous prediction
	 * was determined
	 */
	void reportContextSensitivity(Parser recognizer,
								  DFA dfa,
								  int startIndex,
								  int stopIndex,
								  int prediction,
								  ATNConfigSet configs);
}