org.antlr.v4.runtime.atn

Class SemanticContext

java.lang.Object

org.antlr.v4.runtime.atn.SemanticContext

Direct Known Subclasses:

SemanticContext.AND, SemanticContext.OR, SemanticContext.Predicate

public abstract class SemanticContext
extends Object

A tree structure used to record the semantic context in which an ATN configuration is valid. It's either a single predicate, a conjunction p1&&p2, or a sum of products p1||p2.

I have scoped the SemanticContext.AND, SemanticContext.OR, and SemanticContext.Predicate subclasses of SemanticContext within the scope of this outer class.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	SemanticContext.AND
static class	SemanticContext.OR
static class	SemanticContext.Predicate

Field Summary

Fields

Modifier and Type	Field and Description
static SemanticContext	NONE
SemanticContext	parent

Constructor Summary

Constructors

Constructor and Description
SemanticContext()

Method Summary

Methods

Modifier and Type	Method and Description
static SemanticContext	and(SemanticContext a, SemanticContext b)
abstract boolean	eval(Recognizer<?,?> parser, RuleContext outerContext) For context independent predicates, we evaluate them without a local context (i.e., null context).
static SemanticContext	or(SemanticContext a, SemanticContext b)

Methods inherited from class java.lang.Object

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

Field Detail

NONE

public static final SemanticContext NONE

parent

public SemanticContext parent

Constructor Detail

SemanticContext

public SemanticContext()

Method Detail

eval

public abstract boolean eval(Recognizer<?,?> parser,
           RuleContext outerContext)

For context independent predicates, we evaluate them without a local context (i.e., null context). That way, we can evaluate them without having to create proper rule-specific context during prediction (as opposed to the parser, which creates them naturally). In a practical sense, this avoids a cast exception from RuleContext to myruleContext.

For context dependent predicates, we must pass in a local context so that references such as $arg evaluate properly as _localctx.arg. We only capture context dependent predicates in the context in which we begin prediction, so we passed in the outer context here in case of context dependent predicate evaluation.

and

public static SemanticContext and(SemanticContext a,
                  SemanticContext b)

or

public static SemanticContext or(SemanticContext a,
                 SemanticContext b)

See Also:

ParserATNSimulator.getPredsForAmbigAlts(java.util.BitSet, org.antlr.v4.runtime.atn.ATNConfigSet, int)