Package org.antlr.v4.runtime.atn
Class SemanticContext
java.lang.Object
org.antlr.v4.runtime.atn.SemanticContext
- Direct Known Subclasses:
SemanticContext.Empty
,SemanticContext.Operator
,SemanticContext.PrecedencePredicate
,SemanticContext.Predicate
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.
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Nested Class Summary
Nested ClassesModifier and TypeClassDescriptionstatic class
A semantic context which is true whenever none of the contained contexts is false.static class
static class
This is the base class for semantic context "operators", which operate on a collection of semantic context "operands".static class
A semantic context which is true whenever at least one of the contained contexts is true.static class
static class
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Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionstatic SemanticContext
abstract boolean
eval
(Recognizer<?, ?> parser, RuleContext parserCallStack) For context independent predicates, we evaluate them without a local context (i.e., null context).evalPrecedence
(Recognizer<?, ?> parser, RuleContext parserCallStack) Evaluate the precedence predicates for the context and reduce the result.private static List
<SemanticContext.PrecedencePredicate> filterPrecedencePredicates
(Collection<? extends SemanticContext> collection) static SemanticContext
or
(SemanticContext a, SemanticContext b)
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Constructor Details
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SemanticContext
public SemanticContext()
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Method Details
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eval
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.
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evalPrecedence
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.
SemanticContext.Empty.Instance
: if the predicate simplifies totrue
after precedence predicates are evaluated.null
: if the predicate simplifies tofalse
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.
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and
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or
- See Also:
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filterPrecedencePredicates
private static List<SemanticContext.PrecedencePredicate> filterPrecedencePredicates(Collection<? extends SemanticContext> collection)
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