Class LLkAnalyzer
- All Implemented Interfaces:
GrammarAnalyzer
,LLkGrammarAnalyzer
- Author:
- Terence Parr, John Lilley
- See Also:
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Field Summary
FieldsModifier and TypeFieldDescription(package private) CharFormatter
boolean
protected Grammar
protected boolean
protected Tool
Fields inherited from interface antlr.GrammarAnalyzer
LOOKAHEAD_DEPTH_INIT, NONDETERMINISTIC
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Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionprotected boolean
Return true if someone used the '.' wildcard default idiom.boolean
Is this block of alternatives LL(k)? Fill in alternative cache for this block.boolean
Is (...)+ block LL(1)? Fill in alternative cache for this block.boolean
Is (...)* block LL(1)? Fill in alternative cache for this block.boolean
Is this (...)* or (...)+ block LL(k)?FOLLOW
(int k, RuleEndElement end) Compute the lookahead set of whatever follows references to the rule associated witht the FOLLOW block.look
(int k, ActionElement action) Actions are ignoredlook
(int k, AlternativeBlock blk) Combine the lookahead computed for each alternativelook
(int k, BlockEndElement end) Compute what follows this place-holder node and possibly what begins the associated loop unless the node is locked.look
(int k, CharLiteralElement atom) Return this char as the lookahead if k=1.look
(int k, CharRangeElement r) look
(int k, GrammarAtom atom) look
(int k, OneOrMoreBlock blk) The lookahead of a (...)+ block is the combined lookahead of all alternatives and, if an empty path is found, the lookahead of what follows the block.Combine the lookahead computed for each alternative.look
(int k, RuleEndElement end) If not locked or noFOLLOW set, compute FOLLOW of a rule.look
(int k, RuleRefElement rr) Compute the lookahead contributed by a rule reference.look
(int k, StringLiteralElement atom) look
(int k, SynPredBlock blk) The lookahead of a (...)=> block is the lookahead of what follows the block.look
(int k, TokenRangeElement r) look
(int k, TreeElement t) look
(int k, WildcardElement wc) look
(int k, ZeroOrMoreBlock blk) The (...)* element is the combined lookahead of the alternatives and what can follow the loop.Compute the combined lookahead for all productions of a rule.static boolean
lookaheadEquivForApproxAndFullAnalysis
(Lookahead[] bset, int k) If the first k-1 sets are singleton sets, the appoximate lookahead analysis is equivalent to full lookahead analysis.void
Set the grammar for the analyzerboolean
subruleCanBeInverted
(AlternativeBlock blk, boolean forLexer)
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Field Details
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DEBUG_ANALYZER
public boolean DEBUG_ANALYZER -
tool
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grammar
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lexicalAnalysis
protected boolean lexicalAnalysis -
charFormatter
CharFormatter charFormatter
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Constructor Details
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LLkAnalyzer
Create an LLk analyzer
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Method Details
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altUsesWildcardDefault
Return true if someone used the '.' wildcard default idiom. Either #(. children) or '.' as an alt by itself. -
deterministic
Is this block of alternatives LL(k)? Fill in alternative cache for this block.- Specified by:
deterministic
in interfaceLLkGrammarAnalyzer
- Returns:
- true if the block is deterministic
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deterministic
Is (...)+ block LL(1)? Fill in alternative cache for this block.- Specified by:
deterministic
in interfaceLLkGrammarAnalyzer
- Returns:
- true if the block is deterministic
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deterministic
Is (...)* block LL(1)? Fill in alternative cache for this block.- Specified by:
deterministic
in interfaceLLkGrammarAnalyzer
- Returns:
- true if the block is deterministic
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deterministicImpliedPath
Is this (...)* or (...)+ block LL(k)?- Returns:
- true if the block is deterministic
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FOLLOW
Compute the lookahead set of whatever follows references to the rule associated witht the FOLLOW block.- Specified by:
FOLLOW
in interfaceLLkGrammarAnalyzer
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look
Actions are ignored- Specified by:
look
in interfaceLLkGrammarAnalyzer
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look
Combine the lookahead computed for each alternative- Specified by:
look
in interfaceLLkGrammarAnalyzer
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look
Compute what follows this place-holder node and possibly what begins the associated loop unless the node is locked.if we hit the end of a loop, we have to include what tokens can begin the loop as well. If the start node is locked, then we simply found an empty path through this subrule while analyzing it. If the start node is not locked, then this node was hit during a FOLLOW operation and the FIRST of this block must be included in that lookahead computation.
- Specified by:
look
in interfaceLLkGrammarAnalyzer
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look
Return this char as the lookahead if k=1.### Doesn't work for ( 'a' 'b' | 'a' ~'b' ) yet!!!
If the atom has the not flag on, then create the set complement of the tokenType which is the set of all characters referenced in the grammar with this char turned off. Also remove characters from the set that are currently allocated for predicting previous alternatives. This avoids ambiguity messages and is more properly what is meant. ( 'a' | ~'a' ) implies that the ~'a' is the "else" clause.
NOTE: we do NOT include exit path in the exclusion set. E.g., ( 'a' | ~'a' )* 'b' should exit upon seeing a 'b' during the loop.
- Specified by:
look
in interfaceLLkGrammarAnalyzer
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look
- Specified by:
look
in interfaceLLkGrammarAnalyzer
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look
- Specified by:
look
in interfaceLLkGrammarAnalyzer
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look
The lookahead of a (...)+ block is the combined lookahead of all alternatives and, if an empty path is found, the lookahead of what follows the block.- Specified by:
look
in interfaceLLkGrammarAnalyzer
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look
Combine the lookahead computed for each alternative. Lock the node so that no other computation may come back on itself--infinite loop. This also implies infinite left-recursion in the grammar (or an error in this algorithm ;)).- Specified by:
look
in interfaceLLkGrammarAnalyzer
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look
If not locked or noFOLLOW set, compute FOLLOW of a rule.TJP says 8/12/99: not true anymore: Lexical rules never compute follow. They set epsilon and the code generator gens code to check for any character. The code generator must remove the tokens used to predict any previous alts in the same block.
When the last node of a rule is reached and noFOLLOW, it implies that a "local" FOLLOW will be computed after this call. I.e.,
a : b A; b : B | ; c : b C;
Here, when computing the look of rule b from rule a, we want only {B,EPSILON_TYPE} so that look(b A) will be {B,A} not {B,A,C}.if the end block is not locked and the FOLLOW is wanted, the algorithm must compute the lookahead of what follows references to this rule. If end block is locked, FOLLOW will return an empty set with a cycle to the rule associated with this end block.
- Specified by:
look
in interfaceLLkGrammarAnalyzer
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look
Compute the lookahead contributed by a rule reference.When computing ruleref lookahead, we don't want the FOLLOW computation done if an empty path exists for the rule. The FOLLOW is too loose of a set...we want only to include the "local" FOLLOW or what can follow this particular ref to the node. In other words, we use context information to reduce the complexity of the analysis and strengthen the parser. The noFOLLOW flag is used as a means of restricting the FOLLOW to a "local" FOLLOW. This variable is orthogonal to the lock variable that prevents infinite recursion. noFOLLOW does not care about what k is.
- Specified by:
look
in interfaceLLkGrammarAnalyzer
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look
- Specified by:
look
in interfaceLLkGrammarAnalyzer
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look
The lookahead of a (...)=> block is the lookahead of what follows the block. By definition, the syntactic predicate block defies static analysis (you want to try it out at run-time). The LOOK of (a)=>A B is A for LL(1) ### is this even called?- Specified by:
look
in interfaceLLkGrammarAnalyzer
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look
- Specified by:
look
in interfaceLLkGrammarAnalyzer
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look
- Specified by:
look
in interfaceLLkGrammarAnalyzer
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look
- Specified by:
look
in interfaceLLkGrammarAnalyzer
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look
The (...)* element is the combined lookahead of the alternatives and what can follow the loop.- Specified by:
look
in interfaceLLkGrammarAnalyzer
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look
Compute the combined lookahead for all productions of a rule. If the lookahead returns with epsilon, at least one epsilon path exists (one that consumes no tokens). The noFOLLOW flag being set for this endruleblk, indicates that the a rule ref invoked this rule. Currently only look(RuleRef) calls this. There is no need for the code generator to call this.- Specified by:
look
in interfaceLLkGrammarAnalyzer
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lookaheadEquivForApproxAndFullAnalysis
If the first k-1 sets are singleton sets, the appoximate lookahead analysis is equivalent to full lookahead analysis. -
setGrammar
Set the grammar for the analyzer- Specified by:
setGrammar
in interfaceLLkGrammarAnalyzer
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subruleCanBeInverted
- Specified by:
subruleCanBeInverted
in interfaceLLkGrammarAnalyzer
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