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<?php |
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declare(strict_types=1); |
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namespace Antlr\Antlr4\Runtime\Atn\SemanticContexts; |
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use Antlr\Antlr4\Runtime\Comparison\Hashable; |
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use Antlr\Antlr4\Runtime\Recognizer; |
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use Antlr\Antlr4\Runtime\RuleContext; |
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use Antlr\Antlr4\Runtime\Utils\Set; |
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/** |
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* A tree structure used to record the semantic context in which |
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* an ATN configuration is valid. It's either a single predicate, |
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* a conjunction `p1&&p2`, or a sum of products `p1 || p2`. |
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* |
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* I have scoped the {@see AndOperator}, {@see OrOperator}, and |
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* {@see PrecedencePredicate} subclasses of {@see SemanticContext} within |
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* the scope of this outer class. |
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*/ |
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abstract class SemanticContext implements Hashable |
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{ |
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/** |
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* The default {@see SemanticContext}, which is semantically equivalent to |
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* a predicate of the form `{true}?`. |
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*/ |
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public static function none() : Predicate |
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{ |
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static $none; |
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return $none = $none ?? new Predicate(); |
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} |
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public static function andContext(?self $a, ?self $b) : ?self |
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{ |
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if ($a === null || $a === self::none()) { |
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return $b; |
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} |
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if ($b === null || $b === self::none()) { |
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return $a; |
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} |
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$result = new AndOperator($a, $b); |
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return \count($result->operands) === 1 ? $result->operands[0] : $result; |
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} |
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public static function orContext(?self $a, ?self $b) : ?self |
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{ |
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if ($a === null) { |
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return $b; |
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} |
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if ($b === null) { |
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return $a; |
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} |
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if ($a === self::none() || $b === self::none()) { |
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return self::none(); |
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} |
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$result = new OrOperator($a, $b); |
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return \count($result->operand) === 1 ? $result->operand[0] : $result; |
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} |
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/** |
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* For context independent predicates, we evaluate them without a local |
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* context (i.e., null context). That way, we can evaluate them without |
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* having to create proper rule-specific context during prediction (as |
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* opposed to the parser, which creates them naturally). In a practical |
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* sense, this avoids a cast exception from RuleContext to myruleContext. |
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* |
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* For context dependent predicates, we must pass in a local context so that |
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* references such as $arg evaluate properly as _localctx.arg. We only |
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* capture context dependent predicates in the context in which we begin |
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* prediction, so we passed in the outer context here in case of context |
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* dependent predicate evaluation. |
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*/ |
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abstract public function eval(Recognizer $parser, RuleContext $parserCallStack); |
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/** |
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* Evaluate the precedence predicates for the context and reduce the result. |
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* |
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* @param Recognizer $parser The parser instance. |
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* |
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* @return self|null The simplified semantic context after precedence predicates |
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* are evaluated, which will be one of the following values. |
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* |
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* - {@see self::NONE()}: if the predicate simplifies to |
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* `true` after precedence predicates are evaluated. |
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* - `null`: if the predicate simplifies to `false` after |
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* precedence predicates are evaluated. |
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* - `this`: if the semantic context is not changed |
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* as a result of precedence predicate evaluation. |
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* - A non-`null` {@see SemanticContext}: if the new simplified |
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* semantic context after precedence predicates are evaluated. |
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*/ |
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public function evalPrecedence(Recognizer $parser, RuleContext $parserCallStack) : ?self |
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{ |
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return $this; |
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} |
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/** |
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* @return array<PrecedencePredicate> |
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*/ |
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public static function filterPrecedencePredicates(Set $set) : array |
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{ |
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$result = []; |
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foreach ($set->getValues() as $context) { |
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if ($context instanceof PrecedencePredicate) { |
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$result[] = $context; |
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} |
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} |
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return $result; |
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} |
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abstract public function __toString() : string; |
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} |
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SetBased /
antlr-php-runtime
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