org.antlr.v4.runtime.atn

Class ATNConfig

java.lang.Object

org.antlr.v4.runtime.atn.ATNConfig

public class ATNConfig
extends Object

Represents a location with context in an ATN. The location is identified by the following values:

• The current ATN state
• The predicted alternative
• The semantic context which must be true for this configuration to be enabled
• The syntactic context, which is represented as a graph-structured stack whose path(s) lead to the root of the rule invocations leading to this state.

In addition to these values, ATNConfig stores several properties about paths taken to get to the location which were added over time to help with performance, correctness, and/or debugging.

• getReachesIntoOuterContext(): Used to ensure semantic predicates are not evaluated in the wrong context.
• hasPassedThroughNonGreedyDecision(): Used for enabling first-match-wins instead of longest-match-wins after crossing a non-greedy decision.
• getLexerActionExecutor(): Used for tracking the lexer action(s) to execute should this instance be selected during lexing.
• isPrecedenceFilterSuppressed(): A state variable for one of the dynamic disambiguation strategies employed by ParserATNSimulator.applyPrecedenceFilter(org.antlr.v4.runtime.atn.ATNConfigSet, org.antlr.v4.runtime.ParserRuleContext, org.antlr.v4.runtime.atn.PredictionContextCache).

Due to the use of a graph-structured stack, a single ATNConfig is capable of representing many individual ATN configurations which reached the same location in an ATN by following different paths.

PERF: To conserve memory, ATNConfig is split into several different concrete types. ATNConfig itself stores the minimum amount of information typically used to define an ATNConfig instance. Various derived types provide additional storage space for cases where a non-default value is used for some of the object properties. The create(org.antlr.v4.runtime.atn.ATNState, int, org.antlr.v4.runtime.atn.PredictionContext) and transform(org.antlr.v4.runtime.atn.ATNState, boolean) methods automatically select the smallest concrete type capable of representing the unique information for any given ATNConfig.

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	ATNConfig(ATNConfig c, ATNState state, PredictionContext context)
protected	ATNConfig(ATNState state, int alt, PredictionContext context)

Method Summary

Modifier and Type	Method and Description
ATNConfig	appendContext(int context, PredictionContextCache contextCache)
ATNConfig	appendContext(PredictionContext context, PredictionContextCache contextCache)
ATNConfig	clone()
boolean	contains(ATNConfig subconfig) Determines if this ATNConfig fully contains another ATNConfig.
static ATNConfig	create(ATNState state, int alt, PredictionContext context)
static ATNConfig	create(ATNState state, int alt, PredictionContext context, SemanticContext semanticContext)
static ATNConfig	create(ATNState state, int alt, PredictionContext context, SemanticContext semanticContext, LexerActionExecutor lexerActionExecutor)
boolean	equals(ATNConfig other)
boolean	equals(Object o) An ATN configuration is equal to another if both have the same state, they predict the same alternative, and syntactic/semantic contexts are the same.
int	getAlt() What alt (or lexer rule) is predicted by this configuration
PredictionContext	getContext()
LexerActionExecutor	getLexerActionExecutor()
int	getOuterContextDepth() We cannot execute predicates dependent upon local context unless we know for sure we are in the correct context.
boolean	getReachesIntoOuterContext()
SemanticContext	getSemanticContext()
ATNState	getState() Gets the ATN state associated with this configuration
int	hashCode()
boolean	hasPassedThroughNonGreedyDecision()
boolean	isPrecedenceFilterSuppressed()
void	setContext(PredictionContext context)
void	setOuterContextDepth(int outerContextDepth)
void	setPrecedenceFilterSuppressed(boolean value)
String	toDotString() Returns a graphical representation of the current ATNConfig in Graphviz format.
String	toString()
String	toString(Recognizer<?,?> recog, boolean showAlt)
String	toString(Recognizer<?,?> recog, boolean showAlt, boolean showContext)
ATNConfig	transform(ATNState state, boolean checkNonGreedy)
ATNConfig	transform(ATNState state, LexerActionExecutor lexerActionExecutor, boolean checkNonGreedy)
ATNConfig	transform(ATNState state, PredictionContext context, boolean checkNonGreedy)
ATNConfig	transform(ATNState state, SemanticContext semanticContext, boolean checkNonGreedy)

Methods inherited from class java.lang.Object

finalize, getClass, notify, notifyAll, wait, wait, wait

Constructor Detail

ATNConfig

protected ATNConfig(@NotNull
                    ATNState state,
                    int alt,
                    @NotNull
                    PredictionContext context)

ATNConfig

protected ATNConfig(@NotNull
                    ATNConfig c,
                    @NotNull
                    ATNState state,
                    @NotNull
                    PredictionContext context)

Method Detail

create

public static ATNConfig create(@NotNull
                               ATNState state,
                               int alt,
                               @Nullable
                               PredictionContext context)

create

public static ATNConfig create(@NotNull
                               ATNState state,
                               int alt,
                               @Nullable
                               PredictionContext context,
                               @NotNull
                               SemanticContext semanticContext)

create

public static ATNConfig create(@NotNull
                               ATNState state,
                               int alt,
                               @Nullable
                               PredictionContext context,
                               @NotNull
                               SemanticContext semanticContext,
                               LexerActionExecutor lexerActionExecutor)

getState

@NotNull
public final ATNState getState()

Gets the ATN state associated with this configuration

getAlt

public final int getAlt()

What alt (or lexer rule) is predicted by this configuration

getContext

@NotNull
public final PredictionContext getContext()

setContext

public void setContext(@NotNull
                       PredictionContext context)

getReachesIntoOuterContext

public final boolean getReachesIntoOuterContext()

getOuterContextDepth

public final int getOuterContextDepth()

We cannot execute predicates dependent upon local context unless we know for sure we are in the correct context. Because there is no way to do this efficiently, we simply cannot evaluate dependent predicates unless we are in the rule that initially invokes the ATN simulator.

closure() tracks the depth of how far we dip into the outer context: depth > 0. Note that it may not be totally accurate depth since I don't ever decrement. TODO: make it a boolean then

setOuterContextDepth

public void setOuterContextDepth(int outerContextDepth)

getLexerActionExecutor

@Nullable
public LexerActionExecutor getLexerActionExecutor()

getSemanticContext

@NotNull
public SemanticContext getSemanticContext()

hasPassedThroughNonGreedyDecision

public boolean hasPassedThroughNonGreedyDecision()

clone

public final ATNConfig clone()

Overrides:

clone in class Object

transform

public final ATNConfig transform(@NotNull
                                 ATNState state,
                                 boolean checkNonGreedy)

transform

public final ATNConfig transform(@NotNull
                                 ATNState state,
                                 @NotNull
                                 SemanticContext semanticContext,
                                 boolean checkNonGreedy)

transform

public final ATNConfig transform(@NotNull
                                 ATNState state,
                                 @Nullable
                                 PredictionContext context,
                                 boolean checkNonGreedy)

transform

public final ATNConfig transform(@NotNull
                                 ATNState state,
                                 LexerActionExecutor lexerActionExecutor,
                                 boolean checkNonGreedy)

appendContext

public ATNConfig appendContext(int context,
                               PredictionContextCache contextCache)

appendContext

public ATNConfig appendContext(PredictionContext context,
                               PredictionContextCache contextCache)

contains

public boolean contains(ATNConfig subconfig)

Determines if this ATNConfig fully contains another ATNConfig.

An ATN configuration represents a position (including context) in an ATN during parsing. Since ATNConfig stores the context as a graph, a single ATNConfig instance is capable of representing many ATN configurations which are all in the same "location" but have different contexts. These ATNConfig instances are again merged when they are added to an ATNConfigSet. This method supports ATNConfigSet.contains(java.lang.Object) by evaluating whether a particular ATNConfig contains all of the ATN configurations represented by another ATNConfig.

An ATNConfig a contains another ATNConfig b if all of the following conditions are met:

• The configurations are in the same state (getState())
• The configurations predict the same alternative (getAlt())
• The semantic context of a implies the semantic context of b (this method performs a weaker equality check)
• Joining the prediction contexts of a and b results in the prediction context of a

This method implements a conservative approximation of containment. As a result, when this method returns {code true} it is known that parsing from subconfig can only recognize a subset of the inputs which can be recognized starting at the current ATNConfig. However, due to the imprecise evaluation of implication for the semantic contexts, no assumptions can be made about the relationship between the configurations when this method returns false.

Parameters:

subconfig - The sub configuration.

Returns:

true if this configuration contains subconfig; otherwise, false.

isPrecedenceFilterSuppressed

public final boolean isPrecedenceFilterSuppressed()

setPrecedenceFilterSuppressed

public final void setPrecedenceFilterSuppressed(boolean value)

equals

public boolean equals(Object o)

An ATN configuration is equal to another if both have the same state, they predict the same alternative, and syntactic/semantic contexts are the same.

Overrides:

equals in class Object

equals

public boolean equals(ATNConfig other)

hashCode

public int hashCode()

Overrides:

hashCode in class Object

toDotString

public String toDotString()

Returns a graphical representation of the current ATNConfig in Graphviz format. The graph can be stored to a .dot file and then rendered to an image using Graphviz.

Returns:

A Graphviz graph representing the current ATNConfig.

See Also:

http://www.graphviz.org/

toString

public String toString()

Overrides:

toString in class Object

toString

public String toString(@Nullable
                       Recognizer<?,?> recog,
                       boolean showAlt)

toString

public String toString(@Nullable
                       Recognizer<?,?> recog,
                       boolean showAlt,
                       boolean showContext)