Package org.antlr.v4.runtime.atn

Class AmbiguityInfo

java.lang.Object

org.antlr.v4.runtime.atn.DecisionEventInfo

org.antlr.v4.runtime.atn.AmbiguityInfo

public class AmbiguityInfo
extends DecisionEventInfo

This class represents profiling event information for an ambiguity. Ambiguities are decisions where a particular input resulted in an SLL conflict, followed by LL prediction also reaching a conflict state (indicating a true ambiguity in the grammar).

This event may be reported during SLL prediction in cases where the conflicting SLL configuration set provides sufficient information to determine that the SLL conflict is truly an ambiguity. For example, if none of the ATN configurations in the conflicting SLL configuration set have traversed a global follow transition (i.e. ATNConfig.getReachesIntoOuterContext() is false for all configurations), then the result of SLL prediction for that input is known to be equivalent to the result of LL prediction for that input.

In some cases, the minimum represented alternative in the conflicting LL configuration set is not equal to the minimum represented alternative in the conflicting SLL configuration set. Grammars and inputs which result in this scenario are unable to use PredictionMode.SLL, which in turn means they cannot use the two-stage parsing strategy to improve parsing performance for that input.

Since:

4.3

See Also:

• ParserATNSimulator.reportAmbiguity(org.antlr.v4.runtime.dfa.DFA, org.antlr.v4.runtime.dfa.DFAState, int, int, boolean, java.util.BitSet, org.antlr.v4.runtime.atn.ATNConfigSet)
• ParserErrorListener.reportAmbiguity(org.antlr.v4.runtime.Parser, org.antlr.v4.runtime.dfa.DFA, int, int, boolean, java.util.BitSet, org.antlr.v4.runtime.atn.ATNConfigSet)

Field Summary

Fields

Modifier and Type	Field	Description
private final BitSet	ambigAlts	The set of alternative numbers for this decision event that lead to a valid parse.

Fields inherited from class org.antlr.v4.runtime.atn.DecisionEventInfo

decision, fullCtx, input, startIndex, state, stopIndex

Constructor Summary

Constructors

Constructor	Description
AmbiguityInfo(int decision, SimulatorState state, BitSet ambigAlts, TokenStream input, int startIndex, int stopIndex)	Constructs a new instance of the AmbiguityInfo class with the specified detailed ambiguity information.

Method Summary

Modifier and Type	Method	Description
BitSet	getAmbiguousAlternatives()	Gets the set of alternatives in the decision that lead to a valid parse.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Details

ambigAlts

@NotNull
private final BitSet ambigAlts

The set of alternative numbers for this decision event that lead to a valid parse.

Constructor Details

AmbiguityInfo

public AmbiguityInfo(int decision,
 @NotNull
 SimulatorState state,
 @NotNull
 BitSet ambigAlts,
 @NotNull
 TokenStream input,
 int startIndex,
 int stopIndex)

Constructs a new instance of the AmbiguityInfo class with the specified detailed ambiguity information.

Parameters:

decision - The decision number

state - The final simulator state identifying the ambiguous alternatives for the current input

ambigAlts - The set of alternatives in the decision that lead to a valid parse. The predicted alt is the min(ambigAlts)

input - The input token stream

startIndex - The start index for the current prediction

stopIndex - The index at which the ambiguity was identified during prediction

Method Details

getAmbiguousAlternatives

@NotNull
public BitSet getAmbiguousAlternatives()

Gets the set of alternatives in the decision that lead to a valid parse.

Since:

4.5