org.antlr.v4.runtime.atn

Class SemanticContext

java.lang.Object

org.antlr.v4.runtime.atn.SemanticContext

Direct Known Subclasses:

SemanticContext.Operator, SemanticContext.PrecedencePredicate, SemanticContext.Predicate

public abstract class SemanticContext
extends java.lang.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 A semantic context which is true whenever none of the contained contexts is false.
static class	SemanticContext.Operator This is the base class for semantic context "operators", which operate on a collection of semantic context "operands".
static class	SemanticContext.OR A semantic context which is true whenever at least one of the contained contexts is true.
static class	SemanticContext.PrecedencePredicate
static class	SemanticContext.Predicate

Field Summary

Fields

Modifier and Type	Field and Description
static SemanticContext	NONE The default SemanticContext, which is semantically equivalent to a predicate of the form {true}?.

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 parserCallStack) For context independent predicates, we evaluate them without a local context (i.e., null context).
SemanticContext	evalPrecedence(Recognizer<?,?> parser, RuleContext parserCallStack) Evaluate the precedence predicates for the context and reduce the result.
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

The default SemanticContext, which is semantically equivalent to a predicate of the form {true}?.

Constructor Detail

SemanticContext

public SemanticContext()

Method Detail

eval

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

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.

evalPrecedence

public SemanticContext evalPrecedence(Recognizer<?,?> parser,
                             RuleContext parserCallStack)

Evaluate the precedence predicates for the context and reduce the result.

Parameters:

parser - The parser instance.

parserCallStack -

Returns:

The simplified semantic context after precedence predicates are evaluated, which will be one of the following values.

• NONE: if the predicate simplifies to true after precedence predicates are evaluated.
• null: if the predicate simplifies to false after precedence predicates are evaluated.
• this: if the semantic context is not changed as a result of precedence predicate evaluation.
• A non-null SemanticContext: the new simplified semantic context after precedence predicates are evaluated.

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)